So now that you're on pixiv, you probably want to follow some artists. After all, pixiv is a site just for discovering great artistic talent. The first step is to go to an artist's page. Below the artist's avatar are, usually, four links. You want to click on the first of the raised links:
An artist can actually be added from anywhere within their pages: images, favorites, friends, bookmarked artists, etc. If you can see the artist's avatar, you can generally bookmark them. Once you've clicked the bookmark link, you'll go to a page that will allow you to have the artist added as hidden (非公開) or shown (公開) Once you click the only button, your artist is bookmarked and you're done.
It's nice to have a lot of artists favorited, but eventually you might realize you dislike some of them, or you may feel that 20 pages of bookmarks is a little too much. That's why you can remove some artists from your bookmarks as well. Just go to your bookmarked artist section (see the main page):