Aha! Something I know because I have a Mac!
The best bet is to save your pictures in iPhoto. Then you need to "export" the pictures; I put them somewhere on the desktop because it's easiest to find. Make sure you save in jpeg format. Ensure you resize the pictures so they don't take up a lot of bandwidth. I usually do a 480 (width) x 360 (height) pixel size. When you resize ensure that you lock the "aspect ratio" on the window that appears for sizing the picture. Then you only have to change the width or the height. If you adjust one, the other will adjust automatically. This works great for cropped pictures.
It'll ask you to name the photo before you export, so I'd use a name that doesn't include spaces in it. Sometimes when you upload to websites, it doesn't recognize spaces so it may not upload.
If you're having trouble exporting pictures onto the desktop with what I've given, use "help," and enter in "export photo." A list of questions will come up, and you should be able to find the right particular topic that will tell how to export step by step instead of my abbreviated instructions.
Then you need load them onto a internet site. I use:
Photobucket