My son frequently ask questions about the couple kissing on the TV show last night , Like dad why they are kissing? etc . How would I make him understand in the best way ?

I think its our job as parents to explain properly to our kids that what they saw on TV is not good for them specially kissing scenes. Make them understand that its only for adults and maybe in the future they can understand it thoroughly . Also avoid watching scenes like that when your kids are around try to change the channels to avoid such happenings .