To save a proof for later you must be signed in. Name your proof in the "name your proof" input bar. If you enter a name and the proof is incomplete, the proof will be saved so you can finish it later. If you use a name that has been used before, the old proof will be updated to the new one.
To load proofs from the problem repository you must be signed in. After you load a problem from the respository the "name your proof", "Premises", and "Conclusions" input bars are locked to ensure you are solving a repository problem. To start from scratch, click on the "restart proof checking from scratch" button.
After you load a finished repository problem the "name your proof", "Premises", and "Conclusions" input bars are locked. Finished repository problems are intended to be used for reviewing already solved problems.