We do use the standard decimal format, and you already know it's by grouping things by 10.
In hex, the grouping is in 16, instead of 10.
For the letters, there's no single character for numbers 10 and higher, so letters are used instead.
A=10, B=11, C=12, D=13, E=14, and F=15.
Just like in decimal, we use numbers 0-9.
In binary, we use 0-1 (Binary is base 2)
In hex, we use 0-15 (The numbers 10-15 aren't single characters, so we use the first six letters to substitute the numbers 10-15)
Another example, to convince you a bit...
Convert 83947 to hex:
83947/16 = 5246 r.11
5246/16 = 327 r.14
327/16 = 20 r.7
20/16 = 1 r.4
1/16 = 0 r.1
Rearrange the remainders, and you'll get 1-4-7-14-11. Substitute 14 & 11 with E & B, respectively...
And you'll have 147EB as the hex for 83947.