Assuming you have hydraulic lifters, most do, the process is easy, but messy. Get yourself an extra valve cover. Cut a strip down the center out. Or, go to your parts store, and get a set of oil...
Way too involved to post here. Purchase a repair manual for instructions and details.
There is an order to set lifters according to "the book" which gives details as to which intake and exhaust...
On the older ones you can use a timing light. Newer ones do not have that option. You need to give more info for anyone to help you. What year, make, model?
More information is required to answer this question properly. The best way is to pull the casting # off of the block. Is it a truck 350? car? year? roller? flat tappet?
Here's the "Short" answer. (that means I'm not going into detail on any of the steps)
Remove the head (pull the distributor [Turn the engine to #1-TDC and note the orientation of the rotor so you...