I'm working with QGIS 2.14 Essen with Mac OS X 10.11.6 (El Capitan). I was following along in the training manual where I was learning how to digitize a raster file (tiff format) provided by the training session. I was able to enter the edit mode at one point, but now I find I can no longer activate (toggle) the edit tool. I click on it, but no response. I've removed the raster file as a layer and tried to start over, but unfortunately, I had saved the project before and now I am stuck in this unactivated state. Any thoughts of how I get out of this state? A screenshot is provided.
As Nathan W said, you cannot edit a raster file.
You have to click on your "buildings" layer (which I suppose is what your're trying to digitize), in order to select it. Then pen/edit tool will then activate and you'll be able to draw/digitize features on top of your raster.