Answer:
The subject of a sentence is the doer or is the person that performs the action.
It tells us what the person is doing or what is happening.
Subjects can be found at the beginning or at the middle or at the end of a sentence.
It is important because it tell us about the person and what they are doing in the sentence.
For example:Ella is walking with her mother.
In the sentence it is telling us that Ella is walking with her mother.
Ella is dancing....here it is telling us that she is performing an action which is "dancing" without the subject to tell us the action that is taking place the sentence won't be complete and won't make sense....I hope this helps you....