Conjunctions connect words, phrases, or clauses. "Or" is specifically a coordinating conjunction, meaning it joins elements of equal grammatical rank.
Here are some examples:
* "I want pizza or pasta for dinner." ("Or" connects the nouns "pizza" and "pasta")
* "You can go to the park or stay home." ("Or" connects the verb phrases "go to the park" and "stay home")
* "He is happy or sad." ("Or" connects the adjectives "happy" and "sad")