Both Google and Microsoft offer similar word processing, spreadsheet, and presentation tools, but the full version of Microsoft Office is more robust and capable than Google Drive's online office suite. If you want to convert your Drive files into Microsoft Office ones, Google offers a convenient tool to do so.
For each individual file, you could go to the File > Download as... menu to save a copy of the file in a different format (e.g., Microsoft Word), but if you want to convert all your Drive documents, presentations, and spreadsheets at once, Google Takeout is your friend.
Head to https://www.google.com/settings/takeout and select the data you want to download. In this scenario, you might want to deselect all the options except for Drive, since it could take a long time to have Google create the archive for every other product (Gmail, Calendar, and so on).
With Drive selected, you can choose specific files and folders or all of them. By default, documents will be saved in Microsoft Word format, forms and spreadsheets as Microsoft Excel files, and presentations in Microsoft PowerPoint format.
Hit Next and you can select the archive file type (e.g., .zip) and then start the archive generation process. Once Google lets you know it's done, you'll get a compressed file with all your Drive files saved as Microsoft Office files. Easy peasy.
After extracting the files, you can save them to OneDrive, where they won't count towards your storage space.
[h/t Gizmodo Field Guide]