Add .jars in alternative folder

It's easiest if you have the jar files visible in the package explorer to start with, i.e. within your project directory. At that point, you can just right-click on the jar file, go to the "Build path" section of the context menu, then select "Add to build path".

If the jar file is elsewhere and you don't want to move it, you can right-click on the project, and under the "Build path" part of the context menu, select "Add external archives...". Then find the jar file in the file browser, and hit OK.

All of this can also be done from the project properties dialog, in the Java Build Path section.