It's really hard to screw up. Follow the video.

Make sure you make the initial adjustment on the smallest cog with the cable removed.

Leave the cable tension adjuster screw about 2/3 screwed in since you will most likely need to increase the cable tension than lower it.

Release the shifter to the smallest gear position, leave the chain on the smallest cog.

Then install the cable, pull it tight with your hands and tighten the screw.

If nothing is bent you should be able to shift nearly normally already.

Now go through all gears several times and adjust the tension adjuster in quarter turns each time you get a bad shift until you can verify visually that the rear derailleur is alligned properly under each and every cog and that there is no rubbing and hesitation when shifting.

Oh, and don't forget to apply thin lube. Don't use anything thick on the cogs and the chain, like grease.

Adam