There are only 2 wires that go from the PSU to the motherboard. One will be either a wire with a connector that has two rows of 2 and nothing else on the wire, OR a wire that has two rows of two and another one that looks exactly the same connected to it on the same wire, OR it will be a connector with two rows of 4.
That is the processor power cable. Nothing else looks like that and nothing else will fit if you try to plug it into the hole right next to the processor on the motherboard. You also can't put it in the wrong way easily because it is keyed. That means it only fits in one direction unless you are pushing with extreme amounts of pressure.
You should be able to locate this cable and figure out how to orient it without too much trouble. Worst case scenario you just keep turning it until it goes in.
Nothing else will be connected to that wire so it is pretty hard to mistake for something else.
The other motherboard cable is even harder to mistake. It is always going to be the biggest fattest one there.
It will either be a cord with 2 rows of 10 with another cable on the same wire that is 2 rows of 2 (20 + 4), OR it will be a cable with 2 rows of 12 (24), OR it will be a cable with 2 rows of 10 and nothing else (20).
This cable is also keyed so you can't put it in backwards without using lots of strength to do so.
For that matter, all cords are keyed regardless of what they are. None of them can be plugged in backwards.
Generally, motherboards today all have a port for 24 pins and generally all PSUs have 20+4 connectors, so there is no problem here 95% of the time.
If you get a really old or really bad PSU, it might only have a 20. The computer would likely still turn on, but the board can potentially be damaged through power starvation this way.
If you get a PSU that only has a 24 (not a 20+4) and you have a motherboard with only a 20 slot, you can still stick it in and just let the extra power cables hang off the side and nothing bad will happen. This is an extremely rare case.
In any event, I think if you try it you will find it not to be very hard.