The three conjunctions are coordinating conjunctions, subordinating conjunctions, and correlative conjunctions. Coordinating conjunctions join words, phrases, or independent clauses of equal importance. Subordinating conjunctions introduce dependent clauses that cannot stand alone as complete sentences. Correlative conjunctions work in pairs to connect words, phrases, or clauses with equal weight.
or
and, nor, or, for
conjuctions
And, or, but. Those are the most common.
compound subject
Correlative conjunctions.
A sentence must contain a subject and a verb; it can also have and object and phrases, prepositions, conjuctions, etc
The cat and the dog played together in the park.
There are seven coordinating conjunctions in the English language: for, and, nor, but, or, yet, so.
The other name that we can use for conjunctions is CONNECTORS, ..they connect nouns, adjectives, sentences...etc.
Yes, it is correct to put a comma before the word "once" when it is used at the beginning of a sentence to indicate a specific time or condition. For example: "Once, I was afraid of heights but now I enjoy rock climbing."
If you mean a sentence like: Alex and Becky went to the store. Then this is a simple sentence.