What is IDEs?

Answer 1

From Wikipedia:
An integrated development environment (IDE) is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, build automation tools and a debugger. Most modern IDEs have intelligent code completion.

In short, it provides additionnal capabilities over using just a text editor. For example, Eclipse is a Java IDE.

Answer 2

Thanks

Answer 3

some IDEs for Java and more: Intellij Idea (community is free)
Eclipse (free)
Netbeans (free)

dont forget to install the jdk