If  you  turn the  ignition  &  nothing  happens  then you  may  want to check the connections from your battery to your
starter motor. These 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 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 & 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 to check.

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.