make sure u get the angled feeler gauges or else youll have a serious problem.

process in a nutshell is:
start with the motor at TDC then do cylinder 1, rotate the crank counterclockwise 90degrees then do cylinder 3, rotate another 90 then do cylnder 4 then another 90 and do cylinder 2.

theres obviously a little more too it but youre measuring the clearance between the cam and the rocker