Reading Cookies? or using them

Hi! I have been reading your forum and I find it very insteresting and usefull in general...
Right now I am intrigued about something..Im not quite sure how cookies work so; If you had access to cookies from another computer, and you wanted to retrieve from those cookies the means to access a site or forum through another user or password..how would you?
Let me explain myself better........ =P
I need to access a forum with a supermoderator acount, wich password is stored in a cookie in another computer.. so if i had that cookie, how could i read it or use it? I openned cookies but all i see are strange characters, they seem encrypted files or something.. -forgive my ignorance xD, i know it must sound pretty lame for someone who knows about this-

Thanks in advance for your patience and cooperation

Didn't yo momma ever tell you its not nice to steal someones cookies! (thanks SyntaX****** for that lol)

No im only messing lol.
Basicaly all you have to do is delete your cookie for the website you want and put his there.