well as for the profile photo go into your profile settings and click on edit profile picture it shud come up with a think that shows a little browse box. just click that and add watever pic you like!
with the sig you can do the same click on the edit signiture button on the left of the screen in the edit settings thingy. also you can put in links to other sites and such as well as text.
hope this helped if there is anything that you dont understand please say, sorry if it wasnt much help haha
you just start posting just go in and say "hello I'm (insert user name), I'm new to Mene", and people will talk to you and make sure you read the first page of a charity thats where all the rules and what not are
(:
rylovesyou