About learning new things. Of course it's impossible to learn facts about the world that you didn't know before, and which cannot be attained through reasoning. You can't learn that something you want to buy is going on sale tomorrow, for example, unless you already know, at least on some level.

However, it is possible to learn things that can be figured out through thought. As a simple example, in a dream you may remember that your friend's birthday is 5 days after yours, and your birthday was yesterday, so that must mean your friend's birthday is in 4 days. You might figure that out in the dream. It's new information in a sense because you didn't know before the fact that 'my friends birthday is in 4 days', but you had all the information to figure it out.

Of course it can become more complicated. Someone might be able to figure out something really important, like the answer to an important question in their life. But only if they can arrive at the conclusion by using information they already know and thought.

Also, it's sometimes possible to learn how to do things in dreams, like water ski for example. If your mind can simulate the experience accurately enough, you can practice in your dream and get better at it in real life.