~~Hairline cracks (less than 1/16th of an inch) that are vertical or mostly vertical in poured concrete walls are common and typically not a concern.

Floor cracks are also common and not a concern if they are less than 1/2 inch wide and not heaving or settling.

Settling and temperature changes after construction can put enough stress on these stiff structural components to cause normal cracking.

Cracks in walls that are determined not to be an issue should be sealed to prevent water leaks. Even a small hairline crack can let water through.  Epoxy crack injection waterproofing is a common and effective ways to waterproof basement walls.

In addition, ensure that your grading, gutters and downspouts, and general drainage around your foundation's exterior are fully routing water away from your home

Of course, some cracks are a concern and may need repair.  Horizontal cracks are a sign of soil or water pressure exerting force on the foundation. This type of crack will need significant repairs.

If you are not certain if cracks in your foundation are a concern, contact a qualified foundation repair company or structural engineer