Commas: There's 4 different types of commas. Listing, Joining, Gapping and Bracketing.
Listing example:
You can travel to Spain by Car, Plane or Boat. (Note there isn't a comma after plane because you're putting the last of the 3 options after it.)
Joining example (Used to join to sentences into one):
You must complete your assignment by Friday, or you will not receive a mark.
Gapping example (Used to replace one or more words that may be left out):
Great Britain is famous for its economy, Spain, for its tourist attractions and Poland, for its skiing resorts.
Bracketing example (Used to show a weak interuption in the sentence without disrupting the flow):
England contains, it would seem, some of the best footballers in the world.
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A brief explanation for each one if your're stilll unsure on how to use them:
A listing comma can always be replaced by the word and or or.
A joining comma must be followed by one of the connecting words and, or, but, yet or while.
A gapping comma indicates that you have decided not to repeat some words which have already occurred in the sentence.
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.
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Colons and semicolons:
A colon is commonly used to introduce a list.
Example:
To make the perfect cake you need: flour, eggs and water.
A semicolon is similar to a comma; it's often used to join two sentences together.
Example:
In England they say football; in America they say soccer.
