To post a picture, read the following post -
How to post images .
To create a signature, click on the "Update your Profile" link at the top (in the grey box) or in the tan navigation bar (where the search box is) look for the link labeled "Profile". You should see a field labeled "Signature" which is where you create your signature.
If you have a picture, but need help resizing it or modifying it, post it here and I'll take care of it for you, but it won't be until the evening hours when I'm off work.
If you need help or have any questions, feel free to reply here.