I planted a apple tree this year and someone just told me that we have to have two apple trees for tit to grow apples. They said that the bumblebees will fly from tree to tree spreading the pollen and that's how the trees mate is that true.

It depends. What variety of tree did you plant?
And are there any other apple trees in the neighborhood?

It's true, unless you purchased a tree with multiple grafts ( I've seen it done with stone fruit, so apples can't be far behind. )Just keep in mind that if there are no other apple (including Crab apple) trees around- within about 100 yards- then their pollinators MUST be of a different type ( apples aren't big fans of incest) that blooms at the SAME time. Just look for trees that have the same harvest time and you'll be good.

There are self-pollinating varieties of apple, if he purchased one of those his tree will be OK.