"Help do sth." is a verb, whereas "Help DOING sth." is actually a noun. Help do sth. tends to be used with commands. eg. "Help your mum clean the car" "Help me do my homework" whereas, "help DOING sth" is the object of the sentence. eg. "I need help DOING my homework" "Your mum wants help CLEANING the car" You can see that actually "help DOING sth." is actually just a noun which confusingly contains a verb, but "to help TO DO sth." is a set of two verbs