Once your image is uploaded to Commons or Wikipedia, you will probably want to use it in an article. Simply click Edit on the article you want to include the image in, then add the following where you want the image to appear:
[[File:Image name.jpg|thumb|Caption for the image]]
For example:
[[File:Durdle Door Overview.jpg|thumb|[[Durdle Door]], a [[natural arch]] near [[Lulworth Cove]]|alt=Beach with a large rocky arch over the water]]
The button also works. Notice that the caption can contain links.