How can a member view past and present pledges?
You can give your contacts (who have a user login) access to their Contact Dashboard - and once there they can see Pledges

If you don't have CiviPledge enabled go to Admin > System Settings > Enable components.

If you have enabled it but don't see it you may need to go back to your Permission settings and enable those.

You will also find that when you add a Pledge it offer a SelfService Payments Page option.

Maybe worth reading the chapter in the civi book