The automobile is fast, but the airplane is faster.
Words like and and but are conjunctions.
Conjunctions which connect words, phrases, or clauses of equal grammatical value are called co-ordinating conjunctions.
The most frequent are and, but, or, nor, for.
Subordinating conjunctions are used to join a subordinate clause—noun, adjective, or adverb—to another clause or to some word in another clause. At the same time they show the exact significance and bearing of the subordinate clause.
We heard that the train was wrecked.
He came because I called him.
He remained though he wanted to go.
If it rains I shall stay at home.
Subordinating conjunctions are also sometimes used to join participles or adjectives to the rest of the sentence. In such cases, the participle or the adjective modifies a noun.