Most nosebleeds are not dangerous and are not anything to worry about.
Sometimes nosebleeds can be caused by dry air that dries out the blood vessels in the nose which cracks the blood vessels and then causes the nosebleeds.
Those nosebleeds usually stop and clear up on their own once you get some moisture in the air.
Sometimes nosebleeds happen as a result of an injury to the nose or if you pick your nose and then tear a blood vessel in the nose.
Sometimes nosebleeds can be a sign of something serious if they happen too often and on a regular basis but most times a nosebleed is just an annoyance and nothing bad.