Question: Should I have to add external jar files even I have to use Maven dependencies. I am really new to maven and really cant understand what its actually use for. Please guide me understanding maven.Thank you.

Answer: 
Traditionally , if your project requires to use some open source tools and frameworks , you have to manually download them from those tools' official websites . If you want to use libraries A only , but this libraries A depends on the code from another libraries B , you have to download both libraries A and B. It is very troublesome as you not only have to download the libraries you want to use , but also download any additional libraries that those libraries depend on.

The points of Maven dependency feature is that it solves such problem . You only have to define what libraries you want to use in your project in the configuration file (`pom.xml`) , then Maven will help you to download these libraries automatically and retrieve any additional libraries that those libraries need to work from the public Maven repositories or the repositories you defined in the `pom.xml`.

However ,for commercial and copyright reasons, not all of the commonly used libraries are available on the Maven public repositories .One of the example is the Oracle JDBC Driver .For this case,you have to manually download the library and import it as the external libraries for your project uses .You can also import it to your local Maven repository.
You don't need to add any external libraries manually. You need to add those lib as dependencies in maven, thereafter, maven will handle the library for you.

For example if you need to add `slf4j` external library(jar) to your project as a dependency, add the following to the maven `pom.xml` file.

```
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>com.springsource.slf4j.api</artifactId>
  <version>1.5.6</version>
</dependency>

```

If you have a personal library which is not in any public repositories, then you need to install that jar file to your local maven repository.