try a google for photobucket or imageshack ... register on one of those sites, then upload your images. Finally insert the HTTP address of the image into your post by clicking the "insert image" button on the post page and pasting it into the box that pops up ...
You can edit your signature by clicking the "My Controls" link at the top right of the page, then selecting edit signature on left hand menu ... then design your signiture how you like and add images in the same way.
Be aware there are rules on signature sizes and content. The thread is pinned HERE. Basically dont go putting huge flashing text or massive images, be sensible