If something's pointless, it has no use or makes no sense. Telling yourself that it's pointless to be nervous every time you fly on a plane probably won't solve your fear of flying.
Taking standardized tests in school often feels pointless, and an even more pointless exercise might be listening to your best friends argue about which 1970s rock band was the greatest. When something has a useful purpose or a good reason to exist, it has a point — and when it doesn't, it's pointless. You can also use this adjective to mean "dull" or "blunt."