Here is an example of what a Private Portal looks like. All you will see is the Log in tab:
There is no tab displayed for Open Public Opportunities nor is there any tab for Past Public Opportunities.
From this portal a Vendor may either login to their profile (to see potentially any projects that they've been invited to) or create a brand new registration.
What does an Invited Vendor see when they login?
When the invited Vendor logs into their account they will see the projects which they've been invited to under the Invited Opportunities tab (see below):
If a Vendor hasn't been invited to any bids it will look like the screenshot below: