Pictures used on websites need to load quickly. The fancy term used to discuss this is called image optimisation.

Why?

People browsing the internet are an impatient bunch. When they have to wait for things to load, they have a tendency to move on to a new page.

How?

Images or photos used in websites are measured in pixels (px). Often the photo that has been downloaded from a camera is too big to use on a website. It has a pixel height or width greater than 1200px. An image found in a website normally has a height or width of about 200 to 500px.

So how do I make my pictures smaller?

Typically you would use a photo image editor. This is software that can manipulate an image or photo. On the professional side something like Adobe Photoshop can be used. Images can also be edited online. (http://pixlr.com/editor/)

Most people who are not very computer literate would need to use something more basic than a professional photo editor to edit their images.

Often the software that cames bundled with digital cameras will allow you to crop and resize an image. Most of these programs are targeted to the home user and are simpler to use.

If you do not have such software, you could try Picasa from Google. It offers a simple way to resize images. There are a number of other simple image editors out there, and you are bound to find one that works for you.