As we saw in the introduction, there exist verbs that modify their form and verbs that don't. The first ones are known as plain or invariable verbs. Some examples of these are: "live", "play", "eat".
Amongst the verbs that modify their form we have two groups. On the one hand there are verbs modifying their form according to the subject and the object, as is the case of "help".
"My sister is ill and I'm helping her."
"I'm ill and my sister is helping me."