Current vs voltage. I’m going to use NZ values, US and Europe use different, and compare it to water.
Your wall plug can deliver 240volts at 10 amps – let’s call that a 240m high pipe and watertower that can flow at up to 10 gallons a second. Voltage is how much potential energy it has (240m of gravitational potential energy) amp/current is how fast it flows.
What your power board does is magically divide that 10 gallons into up to 4 potential pipes (4 point plug)
Plug your TV into one point – let’s say 3 amps at 240 volts. The power board makes one pipe that can deliver 3 gallons per second, rest is still sitting there ready. Take note, the height of the pipe didn’t change, only how much of the flow is being used, and only 3 gallons per second are flowing – rest is sitting there chillin.
Let’s plug in something else – a heater. High draw, let’s call it 5 amps. Height hasn’t changed, still delivering 240v, but now 8 gallons per second are being used.
Now I want to plug in something else – my xbox is three amps. Oh no, now we’re sitting at 11 gallons through a 10 gallon pipe!!! What happens? In short, the xbox pulls the water through faster than the pipe can handle. It’s like blowing up a balloon too hard – your cheeks start to hurt as they are doing too much! The wires, board and stuff start to heat up. This makes it harder for the power to flow, the power gets pulled harder, repeat until something melts and the circuit breaks.
Practically speaking, your fuses will blow before then – they detect too much water flowing and close. But a shit mulitboard, wiring or seized fuses happen – and fire.