How to add persistent buffer to rendering post-process pipeline?

I have a shader that reads a whole frame and obtains certain information that should be passed and modified by next processed frame.

No input → Frame #1 → output 1
output/input 1 → Frame #2 → output 2
output/input 2 → Frame #3 → output 3

I don’t know how or where I can find information about how to keep information from the previous frame.

Thanks for your help!