There are many ways to do this, but first, you need some kind of press, preferably a press that has a heated plate to help the oils ooze out.
Some will just take a nug and press it and bamb you have your rosin.
Some will make keif the old school way of cold water hash bags. Then take that keif and then press it in a press.
Pressed concentrates tend to be more costly, but have some of the best flavors.
Remember the Silver Surfer E-Banger is a great machine for concentrates