To set up your gallery click here to add a new album for yourself, give it a name and maybe a description. Ignore everything else, scroll to the bottom and click 'Submit'.
To add a picture go into your album and click 'Add an item to this album', give it a title, choose the file to upload from your computer and click 'Submit'.
To use your picture in a post bring up the details of the picture and copy the 'BBC embed code' (e.g. the SMF ID bit). Paste this on your post where you want the pic to appear. Have a go in the Laboratory first.