I have to disagree with the vacuum gage use, some cams wont get 18hg at idle so I dont see how that can be used as a means to set timing
There are hundreds of posts so just search but in general you just need to get the #1 piston (drivers side front) to TDC and mark your balancer or crank pulley for 0' TDC.
If the engine is already in use you might already have timing marks. Connect the light to the #1 spark wire and point the light at the crank pulley. You might see timing marks already there and somewhat accurate