Doubts with projections


I have many doubts about the projections, I would like to know if you could help me with some of them

What kind of things can I achieve with a projection?
Where can I see more documentation of the tools that exist for these?
Is it possible to filter by day or hour?


This is a good starting point for projection, I am sure you can build on this if you can understand the fundamentals.,-who-doesnt-trust-their-hardware.html