The violin has four strings. Starting from the left, they are called G, D, A and E.
The G-string is the thickest string and makes the deepest sound.
The E-string is very thin and makes the highest sound.
For fun, you can make up a mnemonic to help you remember the names of the strings.
My favourite is Grandma Doesn’t Allow Everything.
… or maybe Grandma Does Allow Everything (if she spoils you).