Hey, devs. I want to put a suit on all the players, so I put my character who was wearing the shirt and pants I wanted in StarterPlayer and renamed the model StarterCharacter. But that just gave the player the whole avatar, not only the shirt and pants. Then, I put only the shirt and pants in the model, but that didn’t give the outfit at all.
So I got a little confused about this. If anyone could help me out that would be very much appreciated! 
StarterCharacter isn’t used for this. The purpose of StarterCharacter is primarily to change how the rig is built, whether you need to change the limbs of the player or have them spawn with other things on them (extra parts, values, all that).
If you want to override clothing, there is an option in Game Settings which allows you to apply default clothing for all players who enter. If you need more than one outfit applied to a player, then you can explicitly change their outfits by using a HumanoidDescription or directly changing (or adding if there is none) their Shirt and Pants instances.
There is actually a way to do this. You can use this plugin:
However, when you insert a Starter Character into the Starter Player, there will be no animations. A way to overcome this problem is to choose the animation that you want and equip it onto your avatar, hit the play button, go to workspace and copy your character, end the testing, and paste your avatar. Then, just use this plugin to customize how you want your avatar to look.