So I just bought a older home with an old sliding honeywell thermostat and I want to install a programmable 3M30. I only have the black & white wire in the wall and the instructions talk about all these different wires. I only have the black & white - not sure what to do? What do I do? Does this thermostat work with just two wires or do I need to buy another one?

Sure ,it`ll work
You need to go to furnace and find out which wire should be red ,that sends low voltage(24V)to the tstat, the other should be white,, so red or whatever to r or rh on new tstat the other wire to w post