If you need a quick reference guide for the UML notation, check one of the following, IMHO, great UML cheatsheets (in no particular order):

Some are quite old but I still like them and the main elements of the UML notation have not changed during all these years (except for the interpretation of the includes and extends relationships in use case diagrams; you should be careful with this).

And if you want to learn more than simple notation details and go deeper in your understanding of your UML language, our selection of UML books may be helpful as well.