Here's how to create a post and pin a post to place your post on the top of the list.
POST CREATING
Step 1: Select a particular class.
Step 2: In the socials tab. Notice the "share with your class" in the middle spot of your screen.
Step 3: Type what you would like to share in your class.
Step 4: Click add button to attach files in your post.
Step 5: Attach the file that you desire to indicate to your post.
Step 6: Finalize and recheck your attached files. If you think you're done, click the post button to proceed.
Step 7: A prompt will appear to confirm your post has been uploaded.
Step 8: Check the latest post in the socials tab to see your post.
PINNING A POST
Step 1: Click on the 3-dot button in the right corner of your created post.
Step 2: Click on "Pin".
Step 3: You will be able now to see your post on top post in the Soials tab.