From Kaanapali, drive north on Rt. 30 past Kapalua, etc. You'll pass the 32 mile marker and shortly thereafter see parking lots and roadside parking. You can use one of these free entrances if you prefer. We prefer to use "Uncle Jimmy's" entrance. It is marked "private property" and you have to pay $5 per party to use it. However, it's an easy walk at ground level through a nice shaded forest and dry creek way, as well as a nice way to meet up with some locals and ask them questions about the best snorkeling spots, etc.
To get to "Uncle Jimmy's", drive across a little bridge, directly before the 33 mile marker and across from the "Adopt A Highway - Ritz Carlton" sign.
Note that Honolua Bay is not a sandy beach. It has a ton of huge boulders which you can sit on, and more importantly, it has an old boat ramp which makes getting in and out of the water a cinch. The waters are usually calm, though not always, and visibility can be outstanding. Snorkeling companies also use this bay as their "turtle towns" because you'll usually see a turtle or two.