There are two ways to do make your Google Drive files available offline. Both can be used simultaneously.
One setting called "File Sync" will save everything in "My Drive" to your laptop automatically.
It uses it's own algorithm to decide which files are commonly used and should be kept.
To turn this on, first open Settings:
Then search for "Drive" and click "Google Drive Settings":
Check the button next to File sync:
The second option lets you ensure specific files and folders are always available offline.
You can click on any folder or file in the Files app and check the "Available Offline" box.
It will automatically store a cached copy on your computer that will be available even without internet.
The little checkbox with a circle there means it's available offline.