Which of the following sentence illustrates correct subject-verb agreement?
1. When he get excited he talk his head off.
2. They talk everything over before they make a decision.
3. Tanya and Julie talks on the phone every day.
4. We talks before he does anything important.

The answer is Sentence 2, "They talk everything over before they make a decision." 

Let's look at sentences 1, 3, and 4 to see what's wrong with them.

======================================================================

1. When he get excited he talk his head off.

The subject is "he," which is singular (one person). A singular
subject requires a singular verb. "Get" and "talk" would be
appropriate if the sentence had a plural subject (such as "they").

This sentence would be correct in either of these forms:

When he gets excited he talks his head off.
When they get excited they talk their heads off.

======================================================================

3. Tanya and Julie talks on the phone every day.

This sentence has a compound subject (two people, Tanya and Julie).
This requires the use of a plural form of the verb.

This sentence would be correct in any of these forms:

Tanya and Julie talk on the phone every day.
Tanya talks with Julie on the phone every day.
Tanya talks on the phone every day.
Julie talks on the phone every day.

======================================================================

4. We talks before he does anything important.

"We" is a plural subject (representing two or more people). The
sentence needs a plural verb.

This sentence would be correct in either of these forms:

We talk before he does anything important.
He talks with me before he does anything important.

======================================================================

Here is a good rule that you may find useful:

"Remember that the English language uses final -s in two different ways: 

 -s added to a noun means plural. 
 -s added to a verb means singular

Subject-verb agreement, then, implies that there's room for only one
added -s in any subject-verb combination."

Subject-Verb Agreement In The Present Tenses
http://webster.commnet.edu/sensen/part2/twelve/present.html

I hope this helps. If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud

Oh, So COOL! :)

First and foremost the subject verb agreement in english depends not
just on the subject being "SINGULAR / PLURAL " but also whether it is
in FIRST/ SECOND / THIRD PERSON.

Examples of subject in the 3 categories :

FIRST PERSON : I, We etc etc
SECOND PERSON : You (yes thats the only one)
THIRD PERSON : he, she, sam , bill etc etc etc.

The answer you got tells you that if the subject is singular then verb
is singular.try these

-> he get excited. 
     (this is an adaptation of your sentece number 1.it is wrong.the
correct form being "he gets excited". gets is the singular form of
get)

but............... try this

-> you get excited.
      (In this sentence though the subject is singular the verb used
is  "gets". this is because when the subject is in SECOND PERSON &
though it is SINGULAR the verb is plural.so the sentence is correct.)

so be advised that its not just the SINGULAR OR PLURAL factor but also
the FIRST/SECOND/THIRD person factor that determines the verb
(singular or plural).

ok lets look at those sentences in detail

so here is an outline of the rules you need

1. FIRST PERSON/ SINGULAR verb is SINGULAR.
    eg :  he gets mad.
2. FIRST PERSON/ PLURAL verb is PLURAL.
    eg : we get mad.
3. SECNOND PERSON / SINGULAR verb is PLURAL
    eg: you get mad.
4. THIRD PERSON / SINGULAR verb is SINGULAR
    eg : Bill gets mad.
5. THIRD PERSON / PLURAL verb is PLURAL
    eg: They get mad.

From the rules it is clear that the verb agrees with the noun being
singular or plural except in the case of SECOND PERSON.

in the light of the rules ive outlines ill tell you whats wrong with the sentences.

1. When he get excited he talk his head off.
     WRONG. SEE RULE 4.

2. They talk everything over before they make a decision.
        CORRECT      

3. Tanya and Julie talks on the phone every day.
          WRONG. SEE RULE 5 

4. We talks before he does anything important.
               WRONG.SEE RULE 2  

Well that settles it. Whaddya think ????

Thank you very much for the five-star rating and the nice tip!

~pinkfreud