hey I’m a new dm and I was wondering what the flat ( the what i think is cardboard) surface the tokens sit on is called and where I can but one

Uhh... can you explain it a little more? I don't know what you are talking about.

What you're look for is usually called Dungeon Tiles. They come in may varieties and packages.

Oh ok thanks

Also sorry for the confusion 

Another common DM tool is the Battle Map. I like Chessix. You can find them on Amazon or most gaming stores.