Proofreading is the act of carefully reading through a piece of text in order to uncover any issues with its legibility, grammar and spelling. It is incredibly important to proofread your copy to make sure it is 100% correct as, while some users may never notice these errors, many others will, and this one little example of unprofessionalism could be all it takes to turn them off your brand or product (either conciously or subconciously).
Before you begin proofreading your article (i.e. going over it with a fine toothcomb), it's important to read it through a few times as a whole. Don't get bogged down in the details at this point, you're simply trying to get a sense of how the whole article flows. Does it read well? Do the sentences and paragraphs sit naturally together and form a logical, easy to follow narrative? You may want to get someone else to read over the article at this stage just to make sure they understand it too, as often it's difficult to be objective about this.
Many people find it easier to read text, especially dense text copy, in a physical format so if this suits you be sure to print out your text to begin with, and keep a pencil to hand to quickly jot down any corrections or changes. Once you begin reading, you'll want to take a number of passes at the text in different 'scopes'. For example in the first pass, focus on the words and sentence structure - are there any double negatives, have you used any words with incorrect meanings, does your word ordering make the individual sentences read as easily as possible? On the next couple of passes, focus on the individual letters and punctation marks - double check commas, apostrophes, spacing and spelling. By going through your text in this structured, methodical manner you'll be sure to pick up on as many errors as possible.
The following are just a few quick tips which you may want to bear in mind. It depends on how you read and absorb information as a person so they won't all apply to everyone.
Hopefully this article has kitted you out with some simple tips which will make proofreading your website copy in the future much more thorough, and much less painless. Good luck!