you need to go to solution explore then in the solution explore you will find references ....left click on the references you will find add references....then go to browse of the window ...there you can select the dll of your interest....and it will get added to you project....
you need to open the the reference dll in view in object browser ....there you will get function defination and corresponding class and all....so by creating the objects for them you can use the function of respective dll.....