To prep a small crack rinse it out with water and allow it to dry thoroughly. Also use a steel scrub brush to knock any loose particles away from the crack. If there is any loose pebbles or particles in the crack or hole use a shop vacuum to remove them.
Use mortar repair in a caulking tube to fill in the small cracks, forcing it into the crack to seal it and prevent water from leaking into the concrete. The tip of the caulking tube will smooth the mortar repair a bit; you can do the rest of the smoothing with your finger.
Using a pointing trowel, push concrete patch into the holes and/or "build" missing segments of concrete, and then smooth the concrete patch out. Remember, even if the edges aren't perfect, repairing the cracks before they get out of hand is the way to go. If you're working at the edge of a swimming pool, hold the container of concrete repair below the area you're working on, to catch any concrete patch you slop around before it falls in the pool.
After the patch has cured use concrete sealer to prevent water from entering the patch and damaging the same spot again. Sealing concrete can prevent damage from occurring as quickly.