Any time you wish to add or change content on your Moodle Page you must "Turn editing on". There are two places to do this on your page.
On the left-hand side in the "Administration" block is a link that says "Turn editing on".
On the upper right-hand side is a button that also says "Turn editing on".
Clicking either of these links will do the same thing. You will notice that there are many new options open to you. When you are finished simply click the links that now say "Turn editing off".