If you wanna start train-ing, this is it for sure.
First off, it has detailed documentation, such as fantastic manuals. The general one goes step-by-step through the basics of the mod. There's even one for the interlocking system, which is also probably sophisticated (I didn't even read it yet, just glanced over it). There's also a wiki, with information about things like additional mods, like the one described in the next line.
Then, there's the trains. The mod comes with none, which means you can pick the ones you want seperately. It may seem complicated at first when the description tells you to take a look at the train gallery, but in reality you can scroll down on this ContentDB page and look at the mods that use the advtrains mod. Then, you can see ones that add trains, such as DlxTrains, which is the one I use, since it offers nice features such as dynamic smoke (smoke appearing only when you're driving) and selectable liveries.
You probably want a place to drive the train around then, and this mod offers not just ordinary tracks, but also their variants, like the ones that are able to go up a slope, some that detect trains and activate mesecons, or whatever the loading, unloading, diamond crossing and others even are! Not only that though, you can also have sandstone and stone brick platforms, signal thingies, and a doctor who sonic screwdriver! (look at general manual after the first track images)
This mod's things (such as tracks) and vehicles in mods such as DlxTrains also have crafting recipes, which allows you to admire training even while you're in your non-creative singleplayer world. Then, you can drive around and have fun while also having a practical way of getting around!
And you'll also probably realise how realistic and advanced (that's in the name) this mod is. On example, there's a reason why it implements its own tracks instead of using the minecart ones, it's because they can make big, realistic turns (they can even go halfway to 45 degrees!). The trains accelerate slower when being attached to wagons. You can open and close its doors... And even get run over! Tip: Speaking of getting run over, by default it drops your inventory, even when you're playing mtg with bones enabled. You can go to Advanced Trains Core settings and change the overrun mode to 'normal' if you still want bones.
But nothing can be perfect, and there are some problems, but only a few. There's no fuel system, which sucks if you wanna get more realistic. When stopping the train, it then still slowly moves forward and then suddenly moves back to where it's supposed to stop, or something like that (Edit: that's the rubberband bug, which is minetest's fault), and sometimes it can get buggy. On example, I accidently broke a piece of track under my train, but for some reason the train then got disabled. The logs told to put a track back under it and restart the server, so I did and guess what? The train appeared on the end of the track, facing it while floating! But luckily, I believe this mod will be stable when normally driving the trains.
In conclusion, this mod is fantastic, offering great manuals and even a wiki. It supports customizability, allowing you e.g. to get trains seperately, like from mods. It has a lot of interesting things, such as different track types and even nice platforms and signals (this mod has an interlocking system). It's even possible to craft its items and trains from popular train extensions in non-creative mode, allowing you to always adore this mod. Oh, and even an interlocking system if you're planning to have this on a server! Basically the go-to if you wanna start training.
If you wanna start train-ing, this is it for sure.
First off, it has detailed documentation, such as fantastic manuals. The general one goes step-by-step through the basics of the mod. There's even one for the interlocking system, which is also probably sophisticated (I didn't even read it yet, just glanced over it). There's also a wiki, with information about things like additional mods, like the one described in the next line.
Then, there's the trains. The mod comes with none, which means you can pick the ones you want seperately. It may seem complicated at first when the description tells you to take a look at the train gallery, but in reality you can scroll down on this ContentDB page and look at the mods that use the advtrains mod. Then, you can see ones that add trains, such as DlxTrains, which is the one I use, since it offers nice features such as dynamic smoke (smoke appearing only when you're driving) and selectable liveries.
You probably want a place to drive the train around then, and this mod offers not just ordinary tracks, but also their variants, like the ones that are able to go up a slope, some that detect trains and activate mesecons, or whatever the loading, unloading, diamond crossing and others even are! Not only that though, you can also have sandstone and stone brick platforms, signal thingies, and a doctor who sonic screwdriver! (look at general manual after the first track images)
This mod's things (such as tracks) and vehicles in mods such as DlxTrains also have crafting recipes, which allows you to admire training even while you're in your non-creative singleplayer world. Then, you can drive around and have fun while also having a practical way of getting around!
--- review continues in comment ---
And you'll also probably realise how realistic and advanced (that's in the name) this mod is. On example, there's a reason why it implements its own tracks instead of using the minecart ones, it's because they can make big, realistic turns (they can even go halfway to 45 degrees!). The trains accelerate slower when being attached to wagons. You can open and close its doors... And even get run over! Tip: Speaking of getting run over, by default it drops your inventory, even when you're playing mtg with bones enabled. You can go to Advanced Trains Core settings and change the overrun mode to 'normal' if you still want bones.
But nothing can be perfect, and there are some problems, but only a few. There's no fuel system, which sucks if you wanna get more realistic. When stopping the train, it then still slowly moves forward and then suddenly moves back to where it's supposed to stop, or something like that (Edit: that's the rubberband bug, which is minetest's fault), and sometimes it can get buggy. On example, I accidently broke a piece of track under my train, but for some reason the train then got disabled. The logs told to put a track back under it and restart the server, so I did and guess what? The train appeared on the end of the track, facing it while floating! But luckily, I believe this mod will be stable when normally driving the trains.
In conclusion, this mod is fantastic, offering great manuals and even a wiki. It supports customizability, allowing you e.g. to get trains seperately, like from mods. It has a lot of interesting things, such as different track types and even nice platforms and signals (this mod has an interlocking system). It's even possible to craft its items and trains from popular train extensions in non-creative mode, allowing you to always adore this mod. Oh, and even an interlocking system if you're planning to have this on a server! Basically the go-to if you wanna start training.
Happy training!