Please note that these notes apply to standard texts in emails, letters, articles, reports, etc. Web pages and graphic listings use all sorts of systems that depend on the wishes of the authors.
Use of capitals : use for proper nouns, place names. St. Andrews, Bill Smith, Russia, etc.
Use of commas [ , ]: to separate clauses or insert extra information, to indicate a list, to ‘reset’ a sentence with a conjunction or time reference at the beginning.
Use of full stops (periods US) [ . ]: to end sentences, to mark abbreviations, to indicate missing information (3 together, dots of ellipsis …).
Use of question marks [ ? ] : duh!
Use of semi colons [;]: to separate two clauses that are themselves complete main clauses/sentences.
Use of colons [:]: to introduce a list, to separate two sentences with more force than a semi colon and less than a full stop. In UK English full stops are followed by a lower-case letter, in US English they are followed by a capital.
Use of parentheses [( ) - -] : as commas above for extra information. Can be indicated by brackets, or (at a pinch) hyphens.
Use of exclamation marks [!]: pretty much as you please!
Use of quotation marks [ " ' ...' " ]: - to indicate you are quoting what has been said: 'I am the greatest', said Muhammed Ali. Can also be used to imply that the claim is not entirely true. The so-called 'genius' just left his mobile phone in the kitchen. Double inverted commas or single ones mean the same thing.
Use of apostrophes [ ‘ ]: to indicate possession (Peter’s pen), or to indicate that a letter is missing (don’t = do not).