If you have subscribed to Microsoft 365, then OneDrive is included in your subscription. OneDrive is Microsoft's online cloud service where you can store, access, edit, and share anything you've stored there. If you save a document in Word, for example, you'll see the option to store it in OneDrive.
It's up to you to decide whether to keep OneDrive or not. I don't think it harms anything be leaving it alone, but that's your choice.
(When my MS 365 subscription ends, I will be uninstalling all the MS apps on my MBA, and switch to using Pages, Numbers, and Keynote only. All these apps can read their Windows counterparts...and, being retired, I don't need to use the Office apps like I used to).