So basically what you do is replace any letter you can, with a number! The only number that does not fit a letter is 9! Here, I'll show you what each number is in letter!:
0 = O 1 = I or L 2 = Z 3 = E 4 = A 5 = S 6 = G 7 = T 8 = 8
Understand? GREAT! Now I will give you some words using 1337 5P34K and you answer them in the comments!