A broom finish is the texture left by pulling a concrete broom across a freshly floated slab, and it's the standard finish for exterior flatwork because the ridges give traction when the surface is wet.
The sequence on a typical driveway or sidewalk goes like this: screed, bull float, wait for the bleed water to go away, edge, tool the control joints, float, then broom. Finishing while bleed water is still on the surface works water back into the top of the slab and weakens it, which is a common cause of dusting and scaling later.
Which way. Broom across the direction people walk or drive, so the ridges work against slipping. On a ramp or a sloped drive, that means across the slope.
How coarse. Light, medium and heavy brooms leave different textures, and customers have opinions. Show them a sample, or at least write "medium broom" on the proposal instead of just "broom."
Air-entrained concrete. Exterior slabs that freeze are usually air-entrained. Finish those with magnesium or aluminum floats and a broom, not a steel trowel. Hard-troweling can seal the surface and lead to blistering and delamination.
Keep it even. Pull the broom in overlapping passes, clean it often, and don't go back over a section once it's started to set. Start curing right after the last pass. Curing compound goes on over the broom texture without hurting it.
A broom finish is the baseline price. Exposed aggregate, stamped and colored finishes cost more in hours and materials. The concrete flatwork guide has more on pricing finishes.