To set the classpath in Eclipse, right-click the project in the package explorer and select Build Path -> Configure Build Path... as shown below:




The following window pops up:





Usually, you add external JAR files to the classpath by clicking the button Add External JARs.... External JARs are JAR files that are outside the project's directory tree. If you want to select JAR files located in the project's directory tree, then click Add JARs...

After selecting the JAR files, click OK. The project is automatically rebuilt and you can use the classes contained in the JAR files you just added to the classpath.