How to make a user to wear a shirt pants hat?

Seems to me like you're trying to run before you know how to walk. Anyway I'm going to make this very brief(No pun intended). Preparation First, open up Roblox Studio and click the tab that says models. Then click on advanced and you should see something called advanced objects. Click that. Also open up the properties and explorer windows.

Hats To make a hat you're going to need an object from there called accoutrement. Name it Hat. Drag it into the workspace. Add a part into it and name it Handle. Play the game in studio and parent the hat to your character. Add a mesh to it to give it the shape of a hat. And there you go.

Shirts/Pants To make a shirt is a bit more complex. You'll need to to get a shirt object from advanced objects and then go to Roblox's website. Find the shirt you want in catalogs and get the numbers in the middle of the website address(Something like 495788834). Then in the properties window with the shirt object selected type this in the ShirtTemplate: rbxassetid:// Subtract 1 from the number from before and add that to ShirtTemplate. You should have something like rbxassetid://495788833. Then play studio and add it to your character. Same routine for pants.

Like I mentioned before, you can't learn how to run before knowing how to walk. Watch alot of tutorials on youtube and ask around the forums if you really wanna make a game.