Either the interviewer or the committee members usually begins by asking simple questions about your background.
First of all, decide what the subject(s) is (are); then you will be able to decide if the verb needs fixing, and how.
http://grammar.ccc.commnet.edu/grammar/sv_agr.htm
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Subject-Verb Agreement
Subject-verb agreement is a grammatical concept that states that the subject and the verb in a sentence should agree in number. In other words, if the subject is singular, the verb should be singular, and if the subject is plural, the verb should be plural.
To determine the correct form of the verb, you need to identify the subject of the sentence and then decide whether it is singular or plural. In the sentence you provided, the subject is "either the interviewer or the committee members."
The word "either" implies a choice between two options, so in this case, you should treat the subject as singular. Therefore, the correct form of the verb should also be singular.
For example, instead of saying "Either the interviewer or the committee members usually begins," you would say "Either the interviewer or the committee members usually begins."
If you are unsure about subject-verb agreement, a helpful resource is the link you provided: http://grammar.ccc.commnet.edu/grammar/sv_agr.htm
This website explains the concept in detail and provides additional examples to further clarify the rules of subject-verb agreement.