Explain what the below example is doing and how is it doing it$.$

SET $/$P M$=$Type $1,2,3,$ or $4$ then press ENTER:

IF $\%$M$\%==1$ GOTO CALC

IF $\%$M$\%==2$ GOTO NOTE

IF $\%$M$\%==3$ GOTO BOTH

IF $\%$M$\%==4$ GOTO EOF