There are Vac or Vdc measurement on the mulitmeter.

How to use them?

Example during troubleshooting on PCB board.When do I use Switch to Vdc or Vac to take the voltage drop?

Masurement can be taken when power is on and off?

 

This might be a good time to read the manual that came with the meter. A manual is usually good about walking you through the do's and don't do's that are specific to your meter.

You will get much more enjoyment out of the meter and it will likely last longer if you read and apply all of the information contained in the manual.

hgmjr

 

Further to hgmjr's comments, for more general information you could always browse the relevant sections in the AAC e-book:

DC Metering Circuits

AC Metering Circuits

Dave