I wouldn't say plugging the PSU is hard, nor will I say it's easy. It's really matching certain numbered plugs to certain number sockets.
First things first is the 20/24 plug which goes into the 20/24 socket. These only insert one way due to the shape of the plugs/sockets. Depending on what mobo you have, you may have have either a 20 or 24 socket board. If you find that you have more plugs per socket (24 plugs verse 20 sockets), have the extra four hang of the left side face the fastener clip or remove the extra if possible.
Next is probably the 4 plug/socket. Again, this only plugs in one way and should clip/snap in.
Depending on what mobo you have, you have have a 8 plug/socket. This one should probably plug in only in one way. If you have a socket, but no matching plug for it, you can leave it for now although you should probably get a PSU that does and try not to push your system in its absence.
Again, depending on what mobo you have, you mave even have a straight four pin, or otherwise, known as a molex socket on the board. Molex plugs are usually used to power misc components/devices on the computer, such as the hard drives and optical drives. This one should also be an easy one as the shape of the plug/socket plugs in only one way. You probably don't have one.
Next, if you have a graphics card, you probably have to attach the 6 plug/socket. Occasionally, though, you might have a card the requires the four pin 'floppy' plug.
Finally, you should plug in all your peripherals that require molexes. These probably include your optical drives, your hard drive, any lighting and any fans that require ones, usually ones not plugged into the mobo.
And, if in the rare occasion that you have one, plug in your floppy drive with the four pin 'floppy' plug.
**As a side note, double check with your manual that you have your case power plugs/pins plugged in correctly into your mobo.
