How to create my own dll and share it others

Question

I have googled this topic and found lots of solution;
I have already used class concept in my project so have idea about that..now i want to create my own DLL and share it with others.
After creating the class everyone suggest me to do the following
 
Go to the command line and type the following.
 
CSC /target:library /out:MyFunctions.dll AddClass.cs
MultiClass.cs FactorialClass.cs
 
Go to the command line option /target:library and ask the C Sharp Compiler/Linker to output a DLL instead of an EXE. It's possible to have a different name for the DLL; for example, /out:MyFunctions.dll directs the compiler to output the DLL with the name MyFunctionsLib; otherwise, it will take the default name from the first .cs file. Here, it's AddClass.dll.
 
I am not getting this above thing..can anyone please help me understand this thing.
Thanks in advance.