This is at the moment pretty hard; there is no prebuilt packages with harmony around systems. However, we are working hard to get proper build system using Maven, with proper weekly builds for each supported platform and bitness, allowing us to do some well tested stable releases for a while.
Using old packages is possible and suggested, I haven’t heard too much complains of them not to work. One option would be to build Jambi by yourself and use this for development. For releases using those prebuilt packages is highly suggested though, since by default packages built from our Git repository has system dependency (Linux only, Windows should work, as there is no package manager to depend to), which quite neatly prevents using the packages in different kind of system.
How to actually program using Jambi
This is field where we have absolutely too little material (please submit some!). Main documentation page links some tutorials, examples and generic documentation in one place.
Contribute menu has some information about contributions. Lastly, community menu links forums and other community releases together, where from you can ask help and help others, or just have some chitty-chatty.