I'm building a M16A1, I have a barrel with no sight base attached.  I ordered a front sight base and front sight bins.  How do I install the sight base and pins?  Is the barrel suppose to have grooves cut in it for the pins?

the fsb should be aligned on the barrel and then drilled through the fsb and the barrel then pins inserted. This should be done by a gunsmith.

This is not generally an end user project.
You would be better off to send it out to ADCO and have them pin it.

Or buy  the fixtures/jigs for use with your drill press...
BRD Engineering

Some barrels have groves and others don't.

The pins are driven in by a mall hammer and held in by friction. They should be tapered for this purpose. Go slow and test fit the base.

To align the gas holes use this trick.
Slide the base on the barrel.
Plug or cover one end of the barrel, taping is good.
Attach an air line to the other end. Turn on the air at low pressure.

Rotate the base until the max flow of air is heard or felt. Mark barrel and base for alignment. Align and tap in the pins to succure the base. Easy.

Good luck.

If it was that easy why do they use alignment fixtures and drill jigs ?

Without those, you would need a little luck.

Drilling and pinning is a mating process, to attach the two parts together.  Mated parts are not generally interchangable.  A barrel with grooves already in it would be unlikely to fit a predrilled front sight base.

This is a more involved gunsmithing type operation and you need some tools and really a drill press to do it reasonably.

Just send it to ADCO. They pricing is reasonable and their turn around time is good.  A friend of mine insisted on having his "gun smith" buddy drill the barrel and FSB for taper pins despite me advising against it... sure enough, he got a canted FSB that was all fucked up. Lol...