I bought an exhaust fan and a combination 2 single pole switches(cooper 271a) Im replacing a single pole switch with just a black and white wire How do I do this

You start by telling us a lot more information.

Are you doing a new install or are you replacing an existing fan?
Where is the source of the power supply coming from?
On the metal plate or on the installation instructions, what amperage is needed?

Is the power going to be feed to the fan through the switch or are you planning to use a switch loop?

The screws on one side of the switch are connected together by a metal tab. Put the wire that is hot (probably white) to that side. Connect the other wire to the other side. Are you trying to switch the fan and the light independently? It's not going to work because you need another wire. You will have to replace the cable from the fan to the switch with 3-conductor cable.