How do I check the voltage on the compressor on the outside condensing unit using a voltmeter without frying myself

All volt meters have insulated probes with only the ends uninsulated. To check the voltage you touch the ends of the probes to the two different wires coming into the A/C, you will have the scale on the meter set to at least 250 volts since you checking for 230volts or less. The higher the scale on the meter you set it at will not matter.
As long as you touch only the plastic part of the probe, you will not get shocked.
Good luck, Mike