Welcome!
We would love help, if you go to our GitHub page, you will find issues that are tagged for easy contributions. These are left for people to get an introduction to the engine. We also have a thread here on the forums for things people can help with: The Contribution Mega-Thread - #22 by Darkchaos
We are also starting our vulkan transition and would love some help: JME3 Vulkan - #46 by tlf30
Last, but perhaps most important we are always looking for people to write articles on the wiki, this is a huge help to everyone.
Again, welcome to the community!
Thank you,
Trevor Flynn