Basic .dll creation questions

I've been writing code in a vb form project for a while, but now it turns out I need to build the code into a .dll file to be used by labVIEW. Long story short I don't really know how to write .dlls, which i've been reading up on, but nonetheless a lot of my code (obviously) doesn't simply import into the .dll project well. Right now my code is acting as a terminal retrieving and writing to a serial port connection, and also writing and retrieving from a MySQL server using mysql.data.mysqlclient.h

Is there any way to include the .h files I need in my .dll, or am I trying to do things that .dll files are incapable of? I apologize if my request is basic and vague. Any help is greatly appreciated, even just links to tutorials that could help me out

Thanks in advance!