Concrete will crack and break as it expands and contracts and the ground below shifts. Gaps are left in between sections of concrete to combat the exapansion cracks. Regardless, cracks will appear and this is to be expected. If there is an unusually high number of cracks in particular area, it may be due to poor drainage. Water soaked soil will expand and contract to greater degree with changes in the temperature. Evaluate the drainage around concrete areas.
For small cracks apply a bead of caulking. The caulking will seal the crack and be able to handle any future movement. If you want the caulking to blend in with the concrete, here is a quick tip. Using a small masonry bit, drill a small hole in the side of the concrete where it will be hidden. Collect the dust as it comes out of the hole. Then apply the bits and dust into the caulking while it is still freshy applied. Work the bit in with your finger and sweep away any excess.