When I select Ariba Proposals and Questionnaires or Ariba Contracts from the drop-down menu in the upper-right corner, I see the message: You do not have the appropriate permissions to access this page. Contact your account administrator to request access to this page.

If you are a sub-user, contact your account administrator to begin collaborating with customers through Ariba Sourcing and Ariba Contracts. In the upper-right corner of the application, click [your initials] > Contact Administrator to view your admin's information.

If you are the administrator of the account, ensure your administrator role has the permission Access Proposals and Contracts:

1. In the upper-right corner of the application, click [your initials] > Settings and select Company Settings.
2. Click Users.
3. Click on the Administrator role. The administrator has all permissions and cannot be edited.
4. If you do not see the Access Proposals and Contracts permission, contact SAP Ariba Customer Support.

You can find more information here: How can I find a contract the buyer sent me for approval?

S2C Administration
SAP Business Network for Procurement & Supply Chain
SAP Business Network for Procurement & Supply Chain > Administration (Buyer & Supplier Account Administration)
Strategic Contracts
Strategic Sourcing
Strategic Sourcing > User Administration