https://en.m.wikibooks.org/wiki/Scrabble/Rules
A simple search on your search engine of choice would have yielded the answer.
Is this what you were looking for?
Each letter has a number on, that's the score for using it.
DL and tl are double and triple letter tiles respectively. You get double or triple the points.
I'm not sure if they added it but in the real game you'd get 50 bonus points if you use all your letters.