On your PC or Mac go to google.com/drive.
How to transfer files on a Chromebook
Step 1
Step 2
Log in with the same account that you use on your Chromebook.
Step 3
Click on the 'New' button.
Step 4
Then select a format like 'Folder upload'.
Step 5
Select all the files that you want to upload.
Step 6
Now log in to the same account on your Chromebook and all those files will be waiting for you.