When you create a request, you're letting other users within your organization that are in need of a certain item. User can respond to your request if they have the item available. You will also get notified if someone makes a listing for that item or something similar.
Creating a request starts just that same as making a listing (learn how to do that here). Make sure you select the "Request" bucket when making your post.
Making a request requires less information than a regular listing since you don't have the item on hand and may not know specific details.
You can add custom tags to your request to get more specific.
You can save your request as a draft and complete it later or hit "Done" and post your request to the rest of your organization.