Determine what genre you are interested in. Genres can include novels, short stories, poems, epics and even nonfiction. Subgenres include science fiction, fantasy, historical fiction, romance, thriller and crime. Search for websites specializing in your genre.
After you have determined your genre, think about what you want to get out of a creative writing website. Do you want to share your work with other writers? Would you like to compete in contests? Or are you more interested in sharpening your skills through tutorial articles? Do web searches with your purpose in mind.
When you have found a creative writing website you wish to join, the website will typically ask you to register---especially if it's a contest. You must usually have a PayPal account to accept any cash prizes from contests.
The website, Creative Writing Contests, lists contests from all over the web. Two Sentence Stories and Writer's Weekly also hold their own contests.
If you are not ready to compete, there are plenty of websites that give creative writing tips. Daily Writing Tips, Writer's Digest and Newbie Writers offer writing advice.
If you're struggling or looking for a critique, several websites have writing communities or offer challenges to help keep your creativity going. Critique Groups for Writers is a forum for all types of writers who want input from others. NaNoWriMo challenges writers to write a novel in a month. Creative Writing Prompts, as its name suggests, gives writers a list of prompts if they're stuck for ideas.
By visiting or joining a creative writing website, you can improve your writing. The more you write and read, the better writer you become. You might also make some money.