You can use iPhoto to publish your photos (and video clips) on the web in several ways:
To Facebook
If you have a free Facebook account, you can publish your photos directly from iPhoto to Facebook (to an album or to your Timeline) with the click of a button. If you name Facebook friends in your photos (using Faces), those friends are notified when you post new photos of them (you just need to provide their Facebook email addresses before publishing). If your Facebook friends add name tags to your Facebook photos, the tags are synced to your iPhoto library, so you can use those photos with the Faces feature. Comments posted to your Facebook photos are also synced to iPhoto.
You can use multiple Facebook accounts with iPhoto. For instructions, see Publish your photos to Facebook.
To Flickr
Flickr.com is a website where you can upload your photos. You can publish photos directly from iPhoto to Flickr, and then use iPhoto to update the Flickr album (add, remove, or edit photos). You can also add photos using the Flickr website, and then sync the new photos to your iPhoto library. For instructions, see Publish your photos to Flickr.
On Twitter
Twitter.com is a social networking site that lets you post short messages, called “Tweets.” You can post a Tweet with a photo attached directly from iPhoto. For instructions, see Share your photos on Twitter.
Using Messages
Messages is a chat application that comes with OS X Mountain Lion v10.8. You can share up to 10 photos at a time directly from iPhoto using Messages. For instructions, see Share your photos using the Messages application.
On your own
In addition to the above methods, you can export your photos to a simple webpage and upload it to your own server.
Choose File > Export, and then click Web Page.