Please register as a user under a (nick)name. Click the Register button in the topmost right button bar on any Wikipedia page. If you like, you can provide your email address. No, you will not be spammed!
You get a user page, a try-out page(Sandbox) and a discussion page
Try the editor in your Sandbox
Click Edit-button
Try a change
Click Preview
Fill in an explanation of your correction/addition
Preparation: please give your photo file an appropriate distinguishing descriptive name, so not PIC001 and the like but rather, e.g., Fountain_in_Akibu_city_centre_2013
Preparation: determine the category on Wikimedia Commons your photo would fit in
If none exists, think of a new photo category to create automatically