In fact, you should work with your grammar book on a regular basis. You may find, though, that grammar books contain unfamiliar technical terms. Don't be put off by them. They're simply tools for talking about particular features of grammar. Once you know what they mean, you'll find them handy and easy to use.
Verbs have many different forms.
First, there are finite and non-finite verb forms. English sees , for example, has the ending - s to agree with the subject he, she or it , and it is present tense as opposed to past tense saw . Non-finite verb forms do not have endings which agree with the subject and do not change for tense. All other verb forms are finite. Finite verbs have endings which agree with the subject of the verb for person and number .