A finite verb can change its form:

To walk
1st person: I walk, walked
2nd person: You walk, walked
3rd person: She walks, walked

The -s in "walks" and the -ed in "walked" are tense markers. Finite verbs can change their tense. Non-finite verbs cannot. Moreover, non-finite verbs don't change form at all, not even in the 3rd person singular:

1st person: I am walking
2nd person: You are walking
3rd person: She is walking

The words "am", "are", and "is" are finite verbs. They carry tense; they change form. The word "walking" does not change form - it can't be a finite verb. It's a non-finite verb. Specifically, it's a participle.

Non-finite verbs
Bare stems: I can walk.
Infinitive forms: I like to walk.
Present participle: I am walking;
Past participle: I have walked; passive: The dog was walked