i cannot understand this grammar chapter .pls teach me....................

Punctuation marks have been well explained in our website. 

Here is a sample explanation of the usage of comma:

Commas can be classified under the following headings:

• Listing commas;

• Joining commas;

• Gapping commas and

• Bracketing commas.

Listing commas can by replaced by the word and or or. Instances of the same are:

• He bought a pen and a pencil and a notebook can be written as He bought a pen, a pencil and a notebook .

• She was intelligent and beautiful and calm and soft-spoken can be written as She was intelligent, beautiful, calm and soft-spoken.

• You can go to London or Paris or Scotland can be written as You can go to London, Paris or Scotland.

Joining commas are always followed by one of the connecting words and, or, but, yet or while:

• The courier was due yesterday, but hasn't been delivered yet.

• She took the flight to Paris, while we travelled to London.

• All the costumes are sold out, but you can take this Santa's cap.

Gapping commas are used to avoid repetition of words which have already occurred in a sentence.

• This is a ripe fruit and this, very sour and unripe.

• It is a very complicated issue, and a serious one too.

Bracketing commas always come in pairs, unless one of them would come at the beginning or the end of the sentence, and they always set off a weak interruption which could in principle be removed from the sentence:

• My husband, a pilot, comes home very seldom.

• He, a fighter, never tries to resolve issues.

• She is a jolly girl, independent like a free bird.