Let me make it simple:

I have a class that allows me to put together two words. You instantiate this class, pass two words to it, and you will get the words added together and capitalized.

You pass "hel" and "lo"

You get "HELLO"

Now, the question is:

How can I make a dll out of that class, so I can later on change some of its functionality without having to compile the whole program again ?

I want a dll for windows and a .so for Linux.

How ?