Import the exCamera.gmez (or .gex) Extension through the GameMaker Studio interface under the Extensions section in the asset tree. Finally, you need to import the obj_ex_camera.object.gmx file also located inside the "Extension" folder of the Extension bundle by right clicking on the GameMaker Studio asset tree, under Objects, and choose the "Add Existing Object" option.
Easing scripts are optional. If you plan on using any easing functions for your camera effects, you must also import the easing scripts (easing.gml) into your project. You may import only the ones you are planning to use.