How can you make an object appear and disappear?

Using triggers is the simplest way. Set up layers in your original (usually the background) file (either Photoshop or Illustrator) with the object you want to make appear/disappear. Set the visibility for these layers to off. When you add a trigger behavior to the layer, it will become visible. Depending on how long you wish it to be visible, you may want to set latch on for that trigger. Add the "fade" behavior to the layer if you wish it to fad in/out when triggered. That's it.

You can certainly have lots of images with triggers to make them appear, but a 'cycle layers' behavior might work as well. There is a cycle pause tag you can put on children so it goes to next image then stops until triggered. That way you only need one trigger (for next page) instead of one per image. If you want it to go blank then show next text, then insert a blank image in the cycle layers. (There are lots of youtube videoes etc on cycle layers.)

There are other options like add the text over the top with premier pro instead of Ch. If you want fades etc between text I would consider prem pro. It has video effects for that sort of thing. Ch does not have much support there.