The word that joins words or two parts of a sentence is called conjunction. Conjunctions only join, they do no other work. The words and, but, or are joining words or conjunctions. They are used to join words as well as sentences.
And is a connecting word that tells you more.
The bird can fly. The bird can hop.
The bird can fly and hop .
Here and is used to join the words fly and hop and tells The bird can fly as well as hop.
Let's look at another example:
But is a connecting word that makes a contrast between two words or sentences.
He hit the ball. He dropped the bat.
He hit the ball but dropped the bat.
Here but is used to join the sentences with unlike ideas.