How to run programms in a package from eclipse

i understand how the vm is looking for programs in a package or jar file to start and i manage this from the command line very well. but within ecipse this is still a closed book to me. can somebody explain the meccano in general for eclipse? and suppose you have some jar files in a package. where do you put these jars, so that you can import them and run in eclipse?

reading the eclipse pdf-documentation was quite beneficial to me, especially the chapter about the classpath variables. anyway, now i can run any package i want from eclipse with a simple import.