The iPhone camera is a 2 megapixel (1,200 x 1,600) digital camera. It has almost no features: no flash, focus or zoom. When you bring up the camera interface, it has only one button, at the bottom of the screen. Press this button and it will take a picture.
Once you have taken a picture, the camera application stores it on your phone in the Camera Roll photo album and gets ready to take another picture. You can also press the button at the bottom left corner to go to the Camera Roll. This is essentially the same as viewing the Camera Roll in the Photo Albums application.
While the camera doesn’t have manual controls, it does adjust automatically to light levels and focus. In indoor low light, it will still take decent pictures as long as the subject is not moving. Outdoors, the camera will take better pictures of moving subjects. Note that there is a slight delay when you take a picture, so you may want to press the button a second before the ideal moment.
From here, you can move back and forward in the Camera Roll, start a slideshow, throw away the picture, or press the button at the bottom left. This will bring up four choices: Use As Wallpaper, Email Photo, Assign To Contact, and Send to Web Gallery.
Note that when you send a photo, the picture sent is a 800×600 version of the 1600×800 image you took. This will reduce the file size of the attachment in the email, and is probably a good thing if you are trying to send a quick snapshot to a friend. But if you are using email to send you photo to a more permanent location, like a Web-based photo album, you may want to instead import the photos into iPhoto and send from your computer.