Tipping a shaft is another term for trimming.

You have to trim the tip section of most shafts prior to installing them into a head.
You can then butt trim the assembled club to the desired playing length.

The amount you trim off the tip depends on what flex you want to make the shaft and what number of club the shaft is going into (3 iron will have less trimmed off the tip than an 8 iron).
Most manufacturers will provide you with trimming instructions for their shafts.