Do i need to focus exposures etc before HDR?

I'm quite new to HDR I understand how its done, but need to know do I set the exposures, white balance iso etc myself or to my taste then it will flash off three images from that one? I'm using a nikon d90

Set your shooting mode to 'Auto Bracketing' (if you have it) and take your pic as normal.
BUT, use a tripod and remote (wired) release.
AB takes 3 different shots at different exposures.
All you have to do is merge them together and tone map them.

On better cameras, Auto Bracketing will give you a choice of 3 or 5 exposures. But you can do the exact same thing without AB.

Regular exposure and then do +1, -1 and if you want five exposures do +2, -2 also with your exposure compensation.

Set ISO to the lowest base value (100 or 200) and use a tripod.

Auto bracket your exposures if possible, if not you'll have to manually adjust exposures between shots. To do this, either shoot in manual and adjust the shutter speed yourself, whilst looking at the light meter or use aperture priority and adjust the EV comp + or - as necessary.

Adjust white balance to taste. Have the aperture fairly narrow (f16 or so) but don't stop right down or you'll degrade the image quality.

You can rely on the autofocus, but if you're shooting landscapes, its often best to manually focus.

Use a remote release to trigger the shutter, or if you don't have one, use the self timer - this will help to reduce vibration (& camera movement) when you press the shutter button.