The two stack commands PUSH and POP are for use when using structured programming..
The stack is 0x30 to 0x7f of the general purpose registers...
When you are doing anything say using R1 and R2 ( which I used in the delay ) and then you need to use these registers elsewhere... We can PUSH R1 and R2 onto the stack... Then once we return to what we were originally doing we can POP the R2 and R1 back so we can carry on....
The order is imperative.. Watch this video...