The short answer is that all cells come from other cells. Cells can only be formed when another cell divides to make 2 "daughter cells" that have the same DNA. Sometimes 2 cells will join to form one, such as a fertilized egg cell. Their DNA is combined in the new cell.

Of course, you might be wondering where the first cell came from. A lot of people wonder about that. Since the first cells formed billions of years ago, and single cells don't leave fossils, that's a tough question. It's possible that there were a few different types of cells that formed around the same time. There's evidence that modern plant and animal cells are a result of two or more kinds of cells joining together.