Click on Interact then Photos on the top bar or open up a photo from Latest Activity or from the Photos in the left most column of the home page. Then click on Add in the little box top right.Then select Browse and find the photos on your computer you want to upload. You can add 8 photos at a time.
Another option is to upload from Flickr, if you have photos on that site. You can set that up from your My Photos page. You can even email photos from your mobile. Just use the email address on the upload page. Each member has an unique emai address.
Once photos are uploaded you can create a folder for them, and edit the captions and title, from the Options box (small grey box on top right of the photo). It is a good idea to add a tag so you can search for the photos- e.g. tag it with the name of the ride or person or place. You can add more than one tag, use commas to separate. Use inverted commas around two word or longer tags. eg lbug, Fred,"south coast tour". You can also map your photo.