Purging C02

I have been made several attempts to kegging and just not gettting it right, but believe I am close.

Currently I am attempting the quick force carbonating method at 30 psi by shaking then letting it sit to settle. When it comes time to drink I heard or have been reading to purge the headspace. I will be serving beer around 8psi. By purging the headspace do I just pull up on the relief valve on keg until its done blowing out C02 or do I just release a little bit and test? Lastly, can I just set at 8psi without purging...is purging necessary? Thanks so much for your input in advance.

You don't need to purge afterward. It will equalize in a day or so. It's for people who have to drink the beer the moment they finish shaking it. However, with that said, it may be hard to get the pressure set at 8 if you don't.