You need to have a hook or thesis statement in the introductory paragraph then at least two or three body paragraphs talking about your topic, And then put a conclusion paragraph that should be your introductory paragraph, but reworded.
Began is the verb because it describes a work or somthing that is happening
In the first sentence “Filling “is a GERUND. The gerund has the function of a noun and in this particular example it is part of the subject of the sentence. In the last sentence “to run” and “to walk” is an INFINITIVE. Finally, in the third one, “riding” is a PARTICIPLE. A participle has the function of an adjective and in this particular example it is part of a participle clause.