The assignee of a submittal package has a limited view into a submittal package. They can see the submittal package attachments, and can see and upload directly to requirements that are a part of that submittal package.
The attachments and requirements will be shown in the portal for them to download. To see the portal yourself, select the Submittal Packages tab and the Submittal Package in question:
Then, click View Submission Portal under the title:
The View Submission Portal will open the portal in a new tab, where the assignee can view Attachments and Upload to Requirements:
Note: this link does not require a Buildr login, and can be sent to anyone who should have access to this submittal package.