If you creating a Java project you are usually need some libraries. For integrating these libraries you go to a download page, download it and add it to the build path of your project. But after integrating you will get sometimes build errors. What is happen?
In this situation your added a library which has some dependencies to other libraries. After finding the other library perhaps you have to add a further library and so on. This situation is very annoying. Because of this there are some build tools. The most famous build tool is Maven.
For using Maven you need to install this tool or you need to use - in the case of Eclipse - a plugin. After this you have to create a XML file. The name of this XML file is pom.xml.
Within the pom.xml you will define all parameters which are needed to build your project. The most important information are the dependencies. For example if you need spring in your project you will add a spring jar file as a dependency. The advantage is now, that the spring jar will be downloaded inclusive all the dependencies from this jar. And if you change for example the version of you spring jar it will also change the version of the needed dependencies.
In Big Projects it is common to use a source control system. In the source control system you will not commit this libraries you will commit only the pom.xml without the Java libraries. All team members will now download the dependencies automatically. This is very comfortable.
Maven uses a own repository for resolving the dependencies. In this repository/website you will find the needed XML snippet for your pom.xml.
If you have a small Java project perhaps you don't want to setup a Maven project. Because for setting up are some steps necessary. Install Maven, add it to the Path variable, specify your JDK. And all developers now, it will not work on the first run.
On this site you can insert one or more dependencies to the textarea and all JARs incl. dependecies will be downloaded.