How to Check-In/Out Items from SharePoint

Navigate to the document in the SharePoint library online.
If you are unsure how to get there, find the folder where the document is located in File Explorer, right-click in a space in the window, and choose View Online. The screen above will appear in your default web browser. If prompted, please log into your web browser.
Find the desired document, hover over the title, and hit the 3-dot menu button at the end of the name. Next, choose More, then choose to Check out. Alternatively, select the checkbox for the document, then select the 3-dot menu button on the top right, and the last choose Check out at the bottom of the menu.
Once the check-out is complete, the indicated red arrow will appear. Next, choose the 3-dot menu butt again, then select Open. Last, choose Open in app to open in the desktop version of Office. Alternatively, you can edit in the web version of Word.
The document will then open. If you are prompted to sign in, sign in with the account that access to the document library. Make the desired changes to the document, then hit save.
When the document is closed, you will receive a box asking if you want to check in the document. Hit Yes. Next a version comments dialogue box will appear, provide the comments then hit OK.
Alternatively, you can check in the document or discard the checkout by going back to either 3-dot menu and choosing More, then the desired choice. If Check in is selected, then a version comments box will appear. If Discard check out is chosen then you will be prompted to confirm.