If you turn the ignition switch & nothing happens then you may want to check the connections from
your battery  to  your  starter motor. These  connections sometimes  get rusty  and  need cleaning.

If your battery is not charging then you  may have a loose alternator belt.  If you hear  a screeching noise then tighten the alternator belt and your battery will get charged.

If  you  turn  the  ignition  and  hear  a  clicking  noise  then  your starter motor gear may be sticking.

Put your car into 4th or 5th and make sure your handbrake is off and gently push your car forwards  and backwards. This sometimes  releases the gear.

If  your  starter motor  is  turning  very  slowly  and your interior lights are dull then you may have a faulty or weak battery. To  check  this  it  is  advised  to  take your battery to an auto electrician who can check it.

Be careful when  considering  a  reconditioned alternator  or  reconditioned starter motor. When the price is too low or when asked for your old unit back in exchange normally means its a recon.