Yes, you need an ordinary volt-ohmmeter available at
Amazon, Harbor Freight and multitudes of other places. Prices vary from the low teens to the hundreds of dollars and you do get what you pay for. There is no need to get an expensive multi function precision meter for this purpose so for the basic needs of checking a few voltages a decent meter with features useful for cars and checking other thing around the house can be found for around $20-25.
Once you have a meter, to measure the places I mentioned select DC volts. Most meters are auto-ranging and you can just connect the wires and measure. Inexpensive meters sometimes are not auto-ranging. If yours has a voltage select range then for best accuracy in the car pick a lower range -- say 25 volts or what ever one of the lower ranges might be -- so the 6v you are expecting to measure will be a third to halfway in that range. As an example of accuracy, if you have selected an appropriate range the reading right across the battery might be 6.310 but if you had selected a higher range the meter would still read but might just say 6v and you would not be able to tell if it was 5.9, 6.0, 6.1, 6.2 etc. A few tenths of a volt makes a big difference with a 6v ignition system.
To take the measurement, for a positive ground car, place the red lead on a good clean metal ground surface and the black lead on the terminal you are going to measure and then read the value. If the meter leads are reversed it would still read but the polarity would be incorrectly indicated. Not an issue here but could be confusing if you were measuring something else.
What I meant in the distributor grounding is many times after a car has sat for long periods of time oxidation, corrosion or rust can form between metal surfaces that would normally be clean. Anything like that can have resistance so instead of two bright shiny surfaces being able to carry a solid voltage at no loss there could be some added resistance and extra resistance anywhere in the wiring is the enemy of 6v ignition systems.
To check you could put the meter on volts and see if there is a big change between readings at two points that should be tightly connected together such as a wire directly running between two terminals. If one terminal read 6.3v and the other was 5.9 you know something has happened and .4 volts disappeared. The most likely suspect then is a corroded or rusty connection.
In this case, to check the distributor ground I would remove the wire from the distributor terminal and set the meter to ohms. With one lead on the clean block and the other on the distributor terminal if the points are open you would read nothing on the meter. If the points are open and you read anything then there is a short in the distributor but if the points are closed then ideally it would read 000 or maybe as high as .1 or .2 ohms. If the reading was much higher than .3 ohms then I would suspect a poor connection such as rust on the distributor mounting clamps or oxidation on the point base to plate connection or between the point contacts or even a poor connection between the points and the outside terminal.
When taking an expected low value ohm reading it is also sometimes good to touch the two meter leads together and see what the meter reads before measuring the component. Sometimes the plugs or connections in the meter leads will add a bit of resistance. As an example, if you measure .1 ohms before touching to the component you are measuring you know to subtract the preliminary meter reading or .1 in this case from the actual value of the final measured reading.
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