There are two different aspects to "gameplay" in RPG Maker 3
; the process of creating your RPG masterpiece, and the process of playing through one of these RPG games.
Most of your time is likely to be spent in the editing part. As many hours as RPG's typically provide in gameplay, you'll find that even with an easy-to-use editor, it takes significantly longer to create an RPG. This is a truism of game development. You must remember that when you purchase a new RPG in a store and take 60 hours or so to play through it, it was created by a team of people (possibly more than 60), who each put much more than 60 hours into the game's creation. Expect to spend a good deal of time fleshing out your game in the editing mode. Even if you have been brooding over your plans for an RPG for quite some time, you'll need to either plan it all out and then create it based on your plans, or just build it piece by piece and explore the editing system as you work. Mind you, taking a complete plan and simply entering it would be significantly quicker.
When you're editing your game, you'll find that using a keyboard for data entry will greatly reduce the amount of time required. Also, if you know what classes, characters, enemies, etc. you want to use throughout the game, it would be more efficient to create all of your classes at the same time, then all of your characters, etc. This will allow you to apply a sort of "assembly-line" processing to your work-flow. (This speeds things up quite a bit.)
When you actually play your game, you will be presented with a 3D RPG where you can move around in a vast area and enter different buildings and interact with characters there. Combat is handled in a turn-based manner; once the order of turns is established, each character or enemy takes their turn whittling their opponents' health away. There are melee weapons, ranged weapons, magic items, multi-targeting attacks, healing spells, offensive spells -- everything you'd expect in an RPG. You can also have several people in your party and you can script events to have new party members join the party as you encounter them along your adventure.
If you get tired of editing and you just want to play a dang RPG game already, you can play the sample game that is included. It's not the deepest storyline, with places such as Sample Castle (which is ruled over by King Sample, of course). What it does do is provide a good example of how to create your own RPG. For one thing, there are tutorial parts that demonstrate different various aspects to making your own RPG's. Additionally, the entire sample RPG is simply an RPG maker "Saved Game"; when you load it, you can play it or go right into editing it and tailoring it to your own whim.