Record repositories aren't like libraries...
you can't browse shelves to find the archives you want to look at.
Archives are unique, and if they are lost or damaged they cannot be replaced. So they are kept securely in strongrooms with the right environmental conditions.
You use the archives in a reading room or, as it is often called, a searchroom. When you ask for an item, it will be brought out for you to use in the searchroom. After you have finished with it, it will be put away safely until it is needed again.
You can look for archives that may be helpful for your research either online or in the archives repository itself.
Most of the archives the record repository holds will be listed in detail in catalogues. These usually tell you about the background of the archive - who created it and why - and describe each individual item within it.