You can use iPhoto to publish your photos (and video clips) on the web in many ways:
To your MobileMe Gallery
If you’re a MobileMe member, you can quickly publish your photos to a public or password-protected website. Family and friends can view your photos and download them, and even add their own photos if you want them to. You can also upload photos taken with your mobile phone or other mobile device. For instructions, see Publish photos to your MobileMe Gallery.
WARNING: MobileMe will be discontinued on June 30, 2012. You will no longer have access to your MobileMe Gallery after that date.
If you have a free Facebook account, you can publish your photos directly from iPhoto to Facebook (to an album or to your Wall) 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.
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.
Design a website in minutes with iWeb, an application included with iLife. Choose from a range of Apple-designed templates to create your own photo website, or use your photos to illustrate a personal blog. Let visitors comment on your images and manage those comments from any computer with an Internet connection. You can publish your iWeb site to your MobileMe account or upload it to the hosting server of your choice. For instructions, see Publish your photos using iWeb.
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.