Blend fades gradually from one visual object to another.
Reveal uses one of 23 different patterns to change from one visual object to another or a randomly selected pattern (the 24th pattern).
Visual Object Transition: how it works
Note that for images, the new image needs to be completely loaded before your transition starts, or you'll not get the effect you meant! This means you'll need to manage your scripts in a way that guarantees that the images are already loaded. Calling your function(s) from the BODY onLoad event is probably the most common way of doing this.
Interpage Transition: how it works
You can transition from one page to another, using the same Blend and Reveal transitions as for images and other objects. Example in a new window.
The difference is in how to tell the page what to do.
Instructions for page transitions are put in a META tag within the HEAD of the document.
The general form is:
Event is one of four events that can control interpage transitions:
Transition is either a Blend or Reveal transition, with the parameters set. Duration has a maximum value of 30 seconds.
(See the Blend and Reveal pages for full syntax for the transitions.)
Note that a transition occurs from one page to the next within the same window or frame! If you change windows or frames, you'll have to setup an initial page from which to change as well as the finish page.