You should start with one pushbutton. Determine the appropriate resistor for its positive side, which you connect to the MCU. Determine how you are going to deal with "switch bounce," which is a common effect one encounters with switch inputs. There are several ways to deal with that, but you must understand the effect of switch bounce and how you can deal with it. Once you have determined how to interface ONE switch, you can then repeat the process for two and then three, and so on. With four switches, it is unlikely you'll need a matrix-scanning arrangement, unless that's what you've been assigned to do.

The 7-segment LED displays can be dealt with as an entirely separate task.

RE