1) Register and Sign-In.

2) Click on "Upload Media" under the User Menu.

3) Use the Gallery Manager to create a new gallery. Just type in the name; the rest of the stuff is optional. If you want others to be able to add pictures to your gallery, click the actions tab, and check "Share this gallery"

4) Go back to Upload Media, and click on Media Manager. 

5) Select your gallery (You can add to existing galleries as well).

6) Click the first grey button, the one with the little star in the top left.

7) Upload however you please. Drag and Drop is the easiest.

8) Add the files & click upload.