To get the board manager we must go to
File > Preferences then, in the "Additional Boards Manager URLs" paste
Then, install it by going to
Tools > Board > Boards Manager... You can find it by scrolling down, or just typing linkit in the search box.
As you can see I have already installed it, but if you haven't make sure you do.
Now all we have to do is select it in
Tools > Board, and in
Tools > Port. As seen here.
Now you can get coding!