where to learn about Stack overflow for a noobie

[SoulsKeeper]

Hello, I need to reverse an encryption on a Gif file and it came to my attention that the category i am looking for is about stack overflow

I am new to this and would love to know where do you think is a good place to get some reliable information about the matter, I need to learn it pretty quickly within a few days if i can so any help in the right direction would be much appreciated!

and if you have a few tips for me I welcome them as well :)

Thank you in advance