The Opportunity Marketplace and Talent Mobility are not equally visible to everyone. What you can see and do depends on your role.
Team Coaches, Unit Coaches, and HR Managers create opportunities. Whoever creates an opportunity is responsible for it and can edit it, delete it, add other responsible people, and review the applications. Every opportunity has at least one responsible person.
HR Managers also see all opportunities across the company and have access to the Talent Mobility statistics.
Employees see the open opportunities under Discover opportunities and apply.
Two more things: employees only see opportunities with the status open, not drafts. And you cannot apply to your own opportunity. A Team Coach creates opportunities for their team, a Unit Coach for their unit, an HR Manager for the whole company.