Where to start

I'm fairly new at javaprogramming, I never used modules before and haven't seen it in school eather.
Now I'm working on a pretty big program that uses several api's.
I thought it wouldn't be a bad idea to split all the apiclients in to seperate modules.
While I do understand the concept, I have no idea where to start,.
It's a standalone springboot application with a javaFX frontend.
My intention is to start a number of threads in my main, running all the clients asynchronously, returning some information to the mainprogram, do some magic there and then start two more threads that have to do something in two of the clients.
Some of the questions I have, like how do you bind it all together? What about dependencies, do I need to specify them for each module seperatly or do they inherrit from the main program?
How are variablevalues passed on from one module to the other or the mainprogram?
Any tips, tricks or easy to follow tutorials would be greatly appreciated.
Sorry for possible spelling or grammar mistakes, as you can guess by my name, I'm not native and learned my English not in school, but from tv

Basically the modules help you to encapsulate your code. If you have one or more packages perform some black box magic, you can hide it behind a public API and have your module explicitly export that API package. Or you can set-up your code as a service provider/consumer via java.util.ServiceLoader. You do have to specify and dependencies in the module-info files for each module, as well as in the build scripts. You also have to be careful to avoid modules depending on each other.

Hope this helps some... it is a bit difficult to find examples but I did find some when I was working on a sample module project. Here is one source I used java modules