To parse verbs:

Give the verb word and tell that it is a verb.
Tell whether it is regular or irregular.
Tell whether it is transitive or intransitive.
Tell the voice, the mode, and the tense.
Tell the number and person of the verb.

Parse the verbs in this sentence:

Sarah has written a letter.

Has written is a verb.
It is transitive and active voice.
It is in common form, indicative mode, and present perfect tense.
The present perfect tense is formed by affixing has which denotes present time .
It is in the third person singular number and agrees with its subject Sarah.

Parse the verbs in this sentence:

She can play.

Can play is the verb.
It is regular and intransitive.
It is poten­tial mode and present tense.
It is in the third person singular number to agree with its subject she.

Parse the verbs in this sentence:

America was discovered by Columbus.

Was discovered is a regular transitive verb in the passive voice.
The subject is represented as acted upon.
It is in the indicative mode and past tense.
It is in the third person singular num.
It agrees with its subject America

Parse the verbs in this sentence:

I love to see the sun shine.

To see is an irregular transitive verb active voice.
It is in the infinitive mode.
It is in the present tense.
It limits love.

Parse the verbs in this sentence:

If they were reading the book.

Were reading is an irregular transitive verb.
It is:

in the active voice.
in the progressive form.
in the subjunctive mode.

Parse the verbs in this sentence:

If they were reading the book.

Were reading is an irregular transitive verb active voice.
It is in the progressive form.
It is in the subjunctive mode.