JSDK download

[Abdul Majid Hussain Mohamed]

Hi I am a Java newbi and I specifically want to learn Servlets. While I reading in a book, I was instructed to download JSDK. Do I have to download it in a separate new folder or to the JDK folder I already use.   Secondally can anybody tell me in briefe what Tomcat is all about and do I need to learn it as well.   Regrads   Haji