In above examples "kar" is used If a verb follows another verb, i.e., one action is followed by another. Like "to go (jana) and see (dekhna)"= ja kar dekhna. to join together (sath milna) and work (kam karna)= sath mil kar kam karna. The suffix "na" is removed from the first verb. More examples: dekh kar chalo (watch out and walk = walk while keeping your eyes open). Tum se mil kar aisa laga (I felt after meeting you). Taste it yourself = eat and see = kha kar dekho.