Hi Christmas,
[quote user="Christmas050873"]I'd like to know more about the mdlSharedCell API. [/quote]
Consult MicroStation SDK documentation, namely MDLAPIFunctionReference.chm.
[quote user="Christmas050873"]Specifically what functions are in it? [/quote]
You did not provide any information what MicroStation version you use, but e.g. MicroStation V8i (SELECTseries 4) SDK documentation provides exact list of available functions.
[quote user="Christmas050873"]Also how do I interface/use them?[/quote]
It's not quite clear what are you asking for, the question is a bit too fuzzy. Every function is described in detail including its purpose and parameters, so it should be clear how to use them. And if a particular functions is not clear, please explain what function is it. Of course for the understanding of MDL API it's required to know C language and also MicroStation internals and data structures like Element Descriptor etc.
With regards,
Jan