Larry has brains.
Larry is a fool.
Larry thinks clearly.
The finite verb can be marked for person, number, tense and mood. The other verb forms (infinitive, inflected infinitive, past participle, present participle) cannot be so marked.
Every clause requires a finite verb; even a clause whose subject is unstated will rarely omit the verb. In general, finding and understanding the finite verb is the key to decoding complex clauses and sentences, and so it is essential that you get familiar with the finite verb paradigms.
In Modern English, finite verbs are marked for tense, but they are only minimally marked for person, number and mood: only the third person present singular is so marked. The situation in Old English is not nearly as complex as in, say, Latin, but its finite verb is much more fully marked than in Modern English. All three persons are distinguished in the present indicative singular:
ic seo I see
þu siehst you see
he siehþ he sees
and the second person is distinguished from the first and third in the past indicative singular:
ic seah I saw
þu sawe you saw
he seah he saw
Further, the plural is distinguished from the singular by distinctive endings, and the subjunctive also has endings of its own. But person is distinguished only in the singular indicative, never in the plural or the subjunctive, and there are only two subjunctive endings. Thus while the Old English verb system is certainly more complicated than the Modern English one, it could be far worse.
You should think of the relative complexity of the Old English verb system as a help in learning the language, not an obstacle. In Modern English the verb generally occurs immediately after its subject, and so it is easy to put subject and verb together. In Old English, on the other hand, subject and verb may be widely separated, and so it is a great help to have the verb unambiguously associated with its subject by agreement of person and number.