imho you need to be able to read dc volts to the hundredths of a volt, ac volts to the hundredths, resistance, and maybe amps. I have used my meter to test battery voltage, test alternator performance (output 14+ volts), check fuses, troubleshoot instruments like wind and depth instruments, check switches on bilge pump float switches, shore power on the dock pedestal, and probably a few more.
I used to have a cheap RadioShack meter but it died a few weeks ago. I replaced it with a harbor freight model to $15 but it didn’t read to the hundredth of a volt, only to the volt. Useless to determine battery state of charge. I returned it and bought a $25 model that seems to work fine for me.
A meter with at least a 4.5 digit display
AC Voltage to at least 600 volts, True RMS preferred also.
Audible Continuity check is a plus also, this can be either the same as or different function than a diode check
Current, i.e. Amperage if you are not use to using a multi meter to measure amperage then get one with a clamp current measurement.
bonuses,i.e. nice to have, back light for the display, frequency measurement and capacitance measurements
Well written instruction in your native language.
I’d start with a meter that reads both AC and DC voltage to a minimum of a tenth of a volt, but one hundredth is nice. I question whether homeowner grade meters are accurate to one hundredth anyway. I fully agree with the comment above that a continuity tester can be very handy, but most have them.
For a beginner, I don’t think Ohms, Amp clamps, etc, are going to matter much. Some will come on the meter whether you want them or not.
Don‘t be afraid of buying a basic meter for now. You seem to need big picture info and nearly any will do. As you gain proficiency, you can go get a fancy model. Having more than one around is pretty common, based on the level of need.
I've found a mid-range (cost wise ~us$60.00) VOM to be sufficient for general use onboard. A few things like HZ and audible continuity are helpful. These days it isn't hard to find a good, reasonably priced meter that will do higher than milliamps AC and DC which is really handy if you have a genset or use shore power.
Gonna cost more but I also agree that a DC clamp option for measuring higher amps is very useful on a cruising boat. Definitely at a minimum a good basic meter is a required tool for a cruising boat. Even if the owner doesn't know how to use it well one can at least give a more knowledgeable person info to help trouble shoot. To me an invaluable tool. It is one on the tools that must go with me on a charter. I have fixed many things on charter boats that would have been difficult or impossible to fix without a meter. And not cause a major inconvenience to my vacation.
If you really want to measure battery voltage, then you need a meter with 2-decimal digits and an accuracy of better than 0.5%. Meters are generally specified as a percent-of-full-scale, which is very often 20 volts. So a 1% meter will read +/- 0.2 volts, AND +/- at least one count in the low-order digit. So a reading of 12.5 volts might actually be somewhere between 12.2 and 12.8 volts.
AC volts only need to be "close." Biggest inaccuracy is that inexpensive AC meters only read "correctly" when measuring a true sine wave. A modified-sine-wave inverter will show about 85 volts when outputting 120 volts RMS. True-RMS meters are more expensive.
Current accuracy would be great, but generally not really needed. Even my really good Fluke clamp on meter is only rated at +/- 1%.
The rest of it is mostly fluff. It might be nice to have frequency, but most inexpensive meters don’t have a lot of range or particularly good accuracy. They’ll tell you it’s about 60 cycles.
Ohms? Most of them don’t read particularly accurately at very low-ohms or at very high ohms. In the middle, again close is usually good enough.
Continuity tester? Nice to have but most are so quiet that I can hear them.