You have 2 options:

Select Let’s choose Files: If you want to save your documents and sign in at the same time.

• Accept the permissions.
• Select the files.
• Enter your email or access to your Facebook account or Google account
• Enter your password.

Select Choose Later: To register your account before saving your files.

• Enter your email or access to your Facebook account or Google account
• Enter your password.
• To save your files, touch the + sign
• Accept the permissions.
• Select the files that you want to save