How can I set the picture (Avatar) by my posts?
This can be set by clicking on your forum account name at the top of the page and clicking on the 'Avatar' link. It is here where you can upload a new one.
How can I set the text (Signature) under my posts?
This can be set by clicking on your forum account name at the top of the page and clicking on the 'edit' link. It is here where you can set this text.