Uploading multiple files at the same time is very similar to uploading a single file. You're simple able to add more than one file to the attachments box at the same time!
As a heads up, any tags you select will apply to the entire upload, so if you want to upload files that should be tagged separately, you may want to consider retagging them after the upload or uploading separately for each differently tagged group of files.
To upload multiple files at once:
Click +Add New.
Click File.
In the To field, select a Recipient and Account.
Select a Tag. If desired, also add a Month and Year.
Drag & drop multiple files, or click Browse and select multiple files.
Click Upload.
Note: Files uploaded outside of a message or task have the option to be marked as Firm Only so clients cannot see the files.