The backend searches and parses data from the USGS database, and parses it into a simplified format that can be easily understood by apps for fetching landsat images. On top of that, the backend is also responsible for keeping track of users, their selected targets, and notifying them when the next acquisition date would happen.
The backend is built in C#, using ASP.NET.
You need to have dotnet installed. Installation procedures can be seen here.