'Бегать' means 'to run regularly' 'Бежать' means 'to run at the moment' HTH

Бежать марафон. Бежать от собаки. Бежать за автобусом. (now, at the moment) Бегать длинные дистанции. (about athletes on trainings. It means that they "бегают" this distance many times) Бегать по утрам. (Obviously every morning)

What is difference between I run and I'm running? =)

It doesn't work because the both words belong to the imperfective aspect. They belong to the groups of the Russian verbs "in one direction" and "in all directions". There are some other verbs of these groups: лететь – летать, ходить – идти, ехать – ездить, плыть – плавать, ползти – ползать, бежать – бегать и т.д.

бегать = usually is used with the plurals - many acts of running or a constant running. so it's a general infinitive about something happening in life in general. a guy who likes to run away from.. . to run by the mornings.. to start running by the mornings бежать = about a particular single process of running somewhere (be that a figurative or a literal one). бежать от страха = to run because of the fear of... to run away from a bear. he runs (бежит) so early because he has an interview.