When you are logged in with admin rights, you see an extra menu in the Gallery, allowing you to create new albums, add new photos etc.
You also see a drop down "Item actions" menu underneath each album and photo.
If you click the "Add Items" menu on the left, Gallery2's AddItems form appears, which you can use to add pictures.
When you are logged in to your Joomla website with admin rights, edit buttons appear near the top of each article, for you to click if you want to make changes.
To add a new article to your Joomla site, you can log in to the administration area (your website address followed by /administrator) and then click on Content Items Manager within the Control Panel.
Within Joomla's Content Manager, click the New button to create a new article.
You can then type in (or copy and paste) your article. Make sure that Published is ticked then click the Save button,.
Your article should appear in the list of latest articles (click Latest Information from the left hand menu, then the relevant topic/category).
The (example) article I created appears at the top of the list, since it is the most recent - click on the link to view it.
As this was just an example article, I deleted it by ticking it in Content Items Manager and then clicking the Trash button.