Reading the in-camera light meter
In Manual mode many cameras show a scale with zero in the middle. The meter is comparing the light it measures with the exposure it considers a normal starting point. Moving towards plus means the camera expects a brighter exposure; moving towards minus means darker.
Zero is not automatically correct
The meter does not know that snow should look bright or a black coat should look dark. Very bright or dark scenes can make a centred reading misleading. Use the meter as information, then judge the photograph and histogram where available.
Metering mode matters
Evaluative, matrix, centre-weighted and spot metering look at different portions of the frame. You do not need to master them all immediately. Start with the camera default and learn spot or centre-weighted metering when a difficult scene gives you a reason.