The Bokeh mode is excellent on the Nokia 8. So, launch the Camera app, then click on the little camera icon that's next to the shutter button (which also has a camera icon).
Next, click on Live Bokeh. You can adjust the blur levels before or even after you take the photo. Just tap on the area you want to focus on and take the photo.
After you take the photo, tap on it in the lower right hand corner, click the edit controls, and choose Edit using "Bokeh editor." From there you can readjust the focus area and blur level of your bokeh shot.