DIY means exactly what it's an abbreviation of, do it yourself. Instead of waiting for someone to publish your writing for you, make a zine. Instead of spending your money on overpriced commercial products made by companies with less-than-stellar practices, make your own clothing, or grow your own food, etc.
The term DIY can apply to anything from woodworking to a life style. The DIY lifestyle has been adopted by thousands of people for reasons as important and varied as the people who live it.