You'll need a multimeter, preferably a model that has 2V range. You should be able to buy a decent multimeter for less than Rs 2000.
A DC offset means the amplifier generates its own DC voltage even when there is no external audio input. In an ideal situation it should be zero, but it's never zero and may vary between +/-2 millivolts. I've lived with about +30 mV DC offset on one channel as I could not reduce it further. It didn't blow my speakers but it was not comfortable.
How to test:
1/ with amplifier powered on, unplug all inputs, or select a source with no input.
2/ Unplug the speaker cables too.
3/ set the multimeter in DC Voltage mode at 2V range.
4/ touch red probe of meter to + terminal of speaker binding post of amplifier (any channel).
5/ touch black probe of meter to - terminal of speaker binding post of amplifier (same channel as red probe).
6/ the reading you see is the DC offset. If the value is >2V, set the range to the next higher range (usually 20VDC). Hopefully you should not need to do this.
Some people prefer to loop (also called short) the inputs. Plug RCA-RCA cable between - and + sockets of left channel (or XLR-XLR, as the case may be). Ditto for right channel.
To add: some preamps and amps have a DC blocking capacitor so that no DC passes to the output, while there are others that are DC-coupled (without DC blocking capacitors in the signal path).