The functions tell you whats needed, and the example screenshots is everything you need. Also there is the example project and that is the best documentation that you can get.
Written text documentation is the worst you can get as it does not stick to the code and is error prone as ****.
What the plugin does is obvious: Its importing/exporting mesh data from/to files.
If you need to know how meshes work and how to transfom them, this is general knowledge not specific to the plugin, that ist available broadly.
Your biggest mistake is to not check the result of the operation that gives clear information about whats wrong.