Three different ways to develop an online presence: Blogging - you can tell people about yourself, what you like, or talk about anything you wish, show photos of your artwork and yourself.
Through a website - you could create your own website about yourself and your art practice, add links to other relevant sites such as your blog, you can add photos of yourself as well as your artwork, a CV if you wish.
Other online communities such as 'thebigidea.co.nz' which is an online community for artists, where they can promote themselves, their work, and let people know of any shows or exhibitions that they may be having etc.
The best option for me I think at this stage would be a blog. Mainly because this is all new to me and I am still learning to use this. But when I am more confident I will certainly try the other options.