OKAY.
There is no great philosophy with the meter. The cables are connected to the two lower sockets (i.e. one to the COM socket, the other to the V?mA socket).
In the photo, you have the selected range of 750 ACV (i.e. you can measure a maximum of 750V AC).
To measure the headphone resistance, you must select the 200? range (the knob should indicate this value).
If you now connect the test leads to the headphone leads, the tester will show the resistance of the headphones. The value read from the display will be expressed in ? and when you write what the measurement result is, you should use this symbol, e.g. 16 ?.
The 200? range allows you to measure 0-200? resistances. If the display shows 1 in the first position, then either the test pins are disconnected or, if they are connected, it means that the resistance between the pins is greater than the measuring range (in this case 200?

and then you need to increase the range by selecting e.g. 2000?.
If, in spite of selecting the highest range, you still have 1 in front of the display, you can assume that the resistance is close to ? (there is no transition) and this is also the value you can write about if you do not want it.
If something unclear, please write.
Andrew