Conjunctions are words that connect words, phrases, and clauses. There are two main types of conjunctions: coordinate conjunctions and subordinate conjunctions. Coordinate conjunctions connect elements of equal rank, such as words and phrases, using words like "and", "but", and "or". Subordinate conjunctions connect clauses of unequal rank using words like "when", "because", "since", and "if". Subordinate conjunctions introduce dependent clauses and include words like "before", "how", "once", and "than".