бегать vs. бежать
There is an exercise in the course and it goes like this:
The children are not playing; they are just running home.
As far as I understood from the explanations in the comment sections, бегать is just running without any destination or direction involved (e.g. for fun or sport); бежать is used when there is direction or destination implied. Many of the other exercises supported this. When they were running to school, it was бежать and when I was simply running very fast it was бегать.
The exercise I quoted up there is translated like so:
Дети не играют - они просто бегут домой.
Isn't this supposed to be бежут? They are obviously running towards home. Have I misunderstood them? When I used бежут, it simply wasn't accepted.
Edit: In the same lesson, there is a sentence "We are running home" which is translated as "Мы бежим домой".
есть, хотеть, дать, создать and бежать are irregular in their conjugation, as well as ошибиться and probably ссать. There are numerous verb whose forms you cannot predict from their infinitive but very few like these, with the overall pattern different from the default schemes.