Hi,
I don't know if you still need the answer, but here's an answer :
First, you have to import MultiChainJavaAPI in your own IDE, you can do it either by a link to the github project or in downloading fom github and import the local sources.
Second, you have to call the MultiChainJavaAPI Project : either you create and jar from MultiChainJavaAPI project and you include the jar in your project (it's the better way to do), or you directly reference MultiChainJavaAPI source code in your project.
If you have question around MultiChainJavaAPI, don't hesitate to ask here :
https://github.com/SimplyUb/MultiChainJavaAPI/issues
Regards,
Hubert