Webmethods on the whole is an integration tool that helps applications within an organization or between two organizations interact with each other. For ex, You can get contents from a database, do all the necessary translations and create a flat file out of it and send it to a secure FTP server hassle free. The same thing if u start doing in Java or any other basic programming language will take you a lot of time and resource. Hope this gives you some basic clarity.
Webmethods on the whole is a vast topic. You have guides avaliable on the empower website - Software AG official website - through which you can download and start off. You cannot learn all the concepts in a short time, but yeah that is where you can start. Please feel free to drop me a note if you still have questions