I agree with Joegr, battery first, recharge it or get a jump. clean, clean, clean the cables, if this starts the car, check the voltage with the engine running. check with multimeter across battery terminals dc 20v, you should see 14v when the alternator is charging, over 15v over charging. if you see less than 14v then not charging. could be bad/old battery, how old is the battery? or alternator not charging. if this is all good then look to the starter connections. always be super careful around electrics, you could get killed.