When you discriminate between two things, you can tell the difference between them and can tell them apart.
The ability to discriminate between similar objects is important. For example, if you want to be a good root farmer, it helps if you can discriminate between a turnip and a parsnip. However, some people take it too far and discriminate against other people, treating them differently based on their physical characteristics or abilities. To be able to discriminate between a turnip and a radish is good, but to discriminate against people is not.