In the English language, a subject with two or more parts is considered a compound subject. The parts of the subject are often joined by "and," such as "the dog and the cat."
To make a present tense verb singular, add an "s" or "es," such as "He loves his wife." "He" is the singular subject and "loves" is the singular form of the verb "love." The present tense, plural verb form of love is just "love," as in "The dogs love their owner." "Dogs" is a plural subject, thus requiring a plural verb. Other examples include, "She is" or "She was" - which is the singular "she" followed by the singular verb present and past verb forms of "be;" and "They are" or "They were" - the plural subject of "they" followed by the plural verb form of the present and past tense of the verb "be."
For the most part, singular subjects require singular verbs and plural subjects take plural verbs. In most cases, compound subjects take the plural form of the verb referring to the subject, such as "The dog and the cat were hungry," not "The dog and the cat was hungry."
Certain compound subjects, often cliches, are considered inseparable and therefore a singular subject, thus requiring a singular verb, such as "Bread and butter was all she served," not "Bread and butter were all she served." Or "Peanut butter and jelly was a last-minute addition to the menu," not "Peanut butter and jelly were a last-minute addition to the menu." Also, if parts of the subject refer to the same thing, such as "My aunt and professional mentor," the subject is to be treated as singular, thus taking a singular verb.
The qualifiers "each" and "every" before a compound subject require it to take a singular verb, such as "Every sandwich, cookie and bag of chips was eaten," not "Every sandwich, cookie and bag of chips were eaten."