I have a european socket and if you saw one you will know that you can plug stuff either way. But american sockets can only be plugged in only one way. So does it matter which way its plugged it because it works no matter what. I heard somewhere they use more power that way but i don't know if that's true
There are two ways to answer this.
No. Voltage is a relative measurement, and in any AC power system (American or European), one voltage oscillates above and then below the voltage of the other. Thus, from the perspective of the appliance, which has connections only to the two prongs of the outlet, it's impossible to tell one from the other, because the system is symmetrical.
However, yes. There are things in the world besides those two prongs. For example, the Earth. In the US, an electrical outlet really looks something like this:
The connection between one half of the outlet and Earth is made near the electrical distribution panel:
Now consider, if someone should touch the half of the outlet connected to Earth, probably nothing bad will happen. However, if he should touch the other half of the outlet, he's likely to get shocked by completing the circuit through some accidental 2nd connection with Earth, or something else touching it (which is about everything).
So although flipping the plug around and inserting it backwards will probably be no problem with regard to the electrical operation of the appliance, it may create a safety hazard by exposing the "hot" half of the outlet, the half not connected to Earth, such that someone might touch it and be shocked.
National regulatory and licensing bodies have different requirements for an appliance to be certified as safe. In particular, the home's wiring can be backwards, or users can force plugs in backwards. Thus, things like double insulation have been developed to render appliances safe even in the presence of a fault like backwards home wiring.
There is a pretty good answer here:
Quoting the accepted answer:
Some systems will employ switches and fuses and such in the input power, and this is best handled by the live connection, not the neutral, so a polarized plug helps ensure this. There are also grounding and 'commoning' issues to be taken into consideration. -Majenko
There is also a good discussion about grounding vs. neutral in the comments. Essentially, the neutral is for returning current to the supply while ground is more for safety at the location. I'm paraphrasing here.
Your question was about the European socket, not about other and polarised sockets.
No, the equivalence of both ways to plug a device to a socket of this type is mandatory by law. CE regulations state the same creeping distances and other means of safety for both pins and all connected circuitry in your home appliances. This is pretty obvious, because you have to rely on the behaviour stated on the boiler plate and/or in the manual of your device regardless of the orientation of the plug. As the electronics in your device will see only the AC voltage between N and L, and they cannot discriminate between both, as there is no way to do so, also power consumption will exactly be the same.
There's only a minor difference when it comes to failures inside your appliances. And only in Class I devices. Suppose you have a washing machine, which has a housing connected to PE (which can't be interchanged when you turn the plug, because it's connected to both prongs protruding from the outlet) and a defect causing one wire of the two potential live/neutral wires to short to the housing.
If the now grounded wire was by accident the live one, your fuse or circuit breaker will blow. If it was the neutral on, it won't and your device will seemingly operate rather normal. A RCD will probably fall within both possible orientations.