Besides creating Google format documents from within your Google Drive, you can (and should) upload locally stored files so that you can access and edit from any device. Most teachers will have a plethora of Microsoft Office file types like Word, Excel, and Powerpoint. You can choose to upload these files and retain the original file types, but this will present a problem when you try to share and collaborate, or push files out to students via Google Classroom. You can upload an individual Word document, but when you go to open the file, you are faced with a preview of the file, and a button at the top of the screen that says "Open with", prompting you to open the Word file using Docs. Upon opening the file with Docs, you are now creating another version of the file, adding to the potential confusion of "which file do I use for...". Then you will likely go into your Drive and delete the Microsoft counterpart. To save you the trouble of doing this incessantly, you can check one tiny box that will save you the trouble going forward.
From within Drive, click the gear cog icon in the upper right>settings>check the box "Convert uploaded files to Google Docs editor format". This will automatically change Word files to Docs, Excel files to Sheets, and Powerpoint files to Slides. Note that in the cases of complicated formatting, some minor changes may have occurred, so check your documents before using them, rather than blindly trusting that they will look like you expect them to.
The video shows how to navigate to the file conversion setting.
Instructional Technology Coach
Middletown Public Schools