Amperage measurements using a analog multimeter
Your use of "mains" hints that you are British? If you are in the UK you will be dealing with 240VAC which is a) very dangerous and b) not measurable by this DC ammeter.

If you want to measure AC current in anything mains-powered you want a clamp-on ammeter - no bare connectors to electrocute you and it's highly unlikely the measuring device will ignite.

You also need a breakout cable - you need to put the clamp around just the hot wire or it won't work. Any specialty shop that sells clamp-on ammeters will also have the cable, if it's not included in the package.

If all you want is the operating and standby wattage of common appliances, it's usually on a label near the power cord. Note that "operating" is usually maximum - for a TV that's full brightness and decently loud.