Hey I hope you are good!
Let me help you to understand this-
It's called double check.
When 2 piece at once check your king it called double check.
In this position- your king getting check by the rook but also by the bishop on a6 (2 piece checking your king at once.
Now if you capture the rook with your rook black can capture your king by Bf1 but capturing king is not allowed xD so it's looks like a checkmate.
Let me know if you understand this I will do my best to explain you!
I was playing a game and i moved my king on f1 thinking that if he move his rook to e1 i can capture with my rook. Why is i that in this position i couldnt capture with my rook? i have been playing for a little while now and i dont understand this at all