Puppet Module Guru Required

Hello

I am in need of puppet guru who can help me:

I have created a puppet module which has many config files under module_name/files/filename.yaml

I have placed this module /etc/puppet/code/environments/common/modules

When I run my puppet agent -t I get an error that variables are not defined although they are in config file.

I also get Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Could not find class xxxxxxx for xxxxxx on node

I need someone who can help me:
- understand what the module structure should be and what is the link between hiera.yaml
- help me fix the issue.

I need some long term help in learning, so if you can tutor that will be great