If I wanted to kick someone with a screen GUI where I would put in the username of player and press enter it would kick. How would I do that?
You will have to show that you've put in a good effort to complete this before asking for help, otherwise you're basically asking for someone to create the whole thing for you. Here's something to get you started.
Create the GUI itself. You will need at least a TextBox so the player can type something, and a TextButton or ImageButton so the player can "submit" their input.
Since kicking a player can only be done via a server Script, and you are (presumably) using a LocalScript to run the GUI, you will have to learn how to pass information between the Client and the Server, using Remotes.
Use what you've learned to kick a player with a specific name in a server Script that gets its input from a LocalScript running on the Client.
im not going to write one for you but here is how you kick people I would recomend using a "for loop" to search for the player in players to avoid errors example:
game.Players.ThisIsAnAccount255:Kick("reason")