Shellac
Shellac is a resin dissolved in alcohol, secreted by the lac bug, harvested in India, and dissolved in denatured ethanol by the can. It is the traditional French-polish finish, the default sealer for furniture, and the most repairable finish in the trade. A shellac finish can be patched with a fresh coat of shellac; the lines disappear. The downside is that shellac is water-marked and alcohol-marked, and the finish dissolves if you spill bourbon on it. Use it for drawer interiors, casework backs, French-polished topcoats, and any surface that needs to be repaired without refinishing. A 1-pound cut is the default; a 2-pound cut is a sealer; a 3-pound cut is a build coat. Wax over it for a soft sheen.
Wax
Wax is a paste (carnauba, beeswax, paraffin) buffed onto a surface. It is the oldest finish, the most forgiving, and the easiest to repair. It is also the softest and the least protective. A wax finish will look beautiful on a dresser and will not survive a wet glass. For a working surface, wax over shellac, wax over oil, or wax over a cured film finish. Wax alone is a finishing-room choice, not a kitchen-table choice.
Oil
Boiled linseed oil, tung oil, walnut oil, mineral oil, and the modern blends (Waterlox, Tru-Oil, Osmo) are all penetrating finishes that cure inside the wood rather than on top of it. Oil is the easiest finish to apply and the easiest to repair. An oil finish is matte, soft, and food-safe when cured. A mineral oil finish is the default for cutting boards, spoons, and anything that touches food. Flood it on, wipe it off, wait 24 hours, repeat. Six coats is the working minimum. Sand lightly between coats with 0000 steel wool or 400 grit.
What to use when
The honest rule: a regional handyman business should own a quart of shellac, a tin of paste wax, a pint of boiled linseed oil, and a quart of mineral oil. That is the entire kit. Everything else is a varnish, a poly, or a product intended for a furniture showroom.