Here's why:
* Conjunctions connect words, phrases, or clauses. "Also" connects an additional idea or thought to what came before.
* Coordinating conjunctions join elements of equal grammatical rank. "Also" joins words, phrases, or clauses that are grammatically similar.
Examples:
* Words: He likes apples, and he also likes oranges.
* Phrases: She went to the store, and she also stopped by the library.
* Clauses: The weather was cold, and it also snowed that day.
Let me know if you have any other grammar questions!