MTG Manager is meant to be a way to track your cards in a variety of locations, whether they be in storage, decks or elsewhere.
This is where files storing information regarding cards is handled.
This is where you will add the file that stores information about the cards you own. It is formatted as a CSV file and only contains a minimal amount of information; just an ID unique to the printing of the card, a code unique to the physical card itself, and a code for the location of the card.
This is where the master database of cards is loaded, the scryfall api is used for this. The first time you load the page the database will be downloaded, you only need to refresh the database if new cards have been released and are not showing up.