I have push button on my dash. Press 4x4 to get into 4x4 mode. I have to get out and manually engage the hubs. Some are automagic. To use low range you need to be at a complete stop with your foot on the brake, and maybe in park or neutral, then press low range.
From 2WD to 4WD High range just push the button, if you are spinning your wheels don't engage the 4WD let off the throttle first then engage the 4WD. 2WD or 4WD high to 4WD Low Range you have to stop shift transmission to neutral then engage the 4WD high range, wait for it to engage, then you can engage low range by pushing the low range button. I don't think you can go direct from 2WD to low range without first going into 4WD high range...someone know for sure? If you have a manual transmission you just have to push the clutch in and you can shift to low range or out of low range while stopped.
If you have the manual locking hubs you'll have to of course lock them first otherwise you won't have 4WD regardless which button you press LOL.