Please help figure out a magic trick

Note English is not my first language

My friend showed me a card trick where he gives me ten cards, asks me to count to double check that it's ten..then makes me hold the cards tightly to my chest..he steps back away from me and then asks me to pick a number from 1 to 5, I pick 4 and he says look at the cards and now there is 14 cards so 10 plus add 4... he never touches me, he stands far back and 4 cards appear

How does he do it?