Air Fuel Ratio (AFR) is the ratio of air to fuel in the combustion chamber during the power stroke. This ratio is very important to know when adding on any type of forced induction, whether it be a super charger or a turbo.
After installing a turbo on your Honda Civic it would be a good investment to install an Air Fuel Gauge to monitor the Air Fuel Ratio while the engine is running. I would also recommend taking your car to a shop that has a Dyno to get it tuned properly, otherwise running your engine too lean will blow it up and you’ll have to rebuild it. Below is a link to D-Series Forums that gives a little bit more information about air fuel ratio while running a turbo.
Click Here for Link to a forum post about air fuel ratio