The squares on your Moodle class page are called "Content Blocks", and most have similar attributes. Text at the top of a content block is called a "Summary". You can change the content of the summary by hitting the "Edit Summary" button, which is usually the first icon you see in a new content block. Note: The top content block of the course is called the "Header Block" but still has all the elements of a normal Content Block.
There are two drop-down menus on every content block: "Add a resource" allows you to create links to files and other information you want to convey to your students in your block; "Add an activity" allows you to create links to quizes and assignments in your block. See the individual entries of these resources and activities for more details.
When you add anything to a content block it will be added to the bottom. You can move the objects in your content block by selecting the up/down arrows on the item. This will display a number of boxes, which are locations you can move the item to. Click on the box where you want it to move.
In order to preview your page click on the "Switch role" drop-down menu and select "Student". This will show you what the page will look like to your students.