Joining Compound Sentences With and, but, or....

A compound sentence is made by joining two simple sentences. These two simple sentences are joined by a coordinating conjunction.
Using and to join two sentences.
We can use and  to join two sentences that are alike or to join one which gives extra information to the other.
example : Ears are all different. Each characteristic has a meaning.
               Ears are all different, and each characteristic has a meaning
note : we use a comma before and.
Using but  to join two sentence.
We can use but to join two sentences that give opposite information or to join a positive sentence and a negative sentence which talk about the same subject. ( + but - ) ; (- but + )
example : Other parts of the face changes as we get older. Ears do not change shape.
               Other parts of the face changes as we get older, but  ears do not change shape.
note : we use a comma before  but.
Using or  to join two sentences that give a choice or alternative.
example : Ears that always red mean that person may have a bad temper.
               He/She must just have high blood pressure.
               Ears that always red mean that person may have a bad temper, or he/she may just have high blood 
               pressure.
note : We only use a comma with  and, but, or in compound sentences. when we use and, but, or in simple sentences we do not use a comma.