How would I get user input from a GUI and store it into a value?

I'm trying to create a tag system that will ask for a team name and place it above your head in a billboard GUI, but the problem is, I don't know where to start.

Could someone possibly start me off and help guide me in the direction of finishing this?

This is not a requesting site so you will have to ask somewhere else but this should help you

Billboard GUI

If then statements

Then to actually have something above someones head you could use something like this

--reference the player
if player.TeamColor == BrickColor.new "Brick color here" then
text.Text = [WHATEVER YOU WANT GOES HERE]