You really don't need to worry about the TV or fridge as they only use a little, but a microwave can be 500-800 watts depending on the size, so you should not use it along with a heater, or kettle, or hairdryer or similar. Anything that "heats" always uses a lot and should be used with caution. Most sites will be OK with a 2 kw heater if used alone.
From what I remember at school ( too many years ago...) you divide the power by the AC voltage to get the current - eg 2000W divided by 240V equals 8.3Amps.