If you are satisfied with mere 10% of it then you shouldn't try to learn it from UML book. Rather, you better read a good book on object-oriented analysis or design patterns -- these books provide you with the 10% you are looking for.
If you are nonetheless looking for a tutorial for UML I would recommend this webpage, and especially this essay on UML diagrams (It's not an ad, I personally have no relation to this site whatsoever). Just browse through the diagrams and look at them: they are mostly self-explaining and you can easily understand what they are depicting as long as you are aware of OOP and generally program design and architecture.
Why would I recommend exactly this page? (asked in the comment)
There are several reasons why I liked it more than the others:
- It presents you an overview table of UML diagrams on the very first page.
- This table, apart from giving the short description of every UML2.0 digramm, also has a very useful column "Learning Priority" that can help a UML-beginner to identify the most often used UML diagrams.
- Even though it contains machine-rendered diagrams as well, most diagrams look like being hand-drawn (probably they are hand-drawn). I take it as a sign that modelling can still be done using only your pencil and paper, no need to delve into UML visualisation software in the very beginning.