Here are the most professional tips about how to tell which Screen part you need for the Nexus 5:
LCD Only: If the image under the glass is broken and the touch screen is NOT then you only need a Nexus 5 LCD screen.
Digitizer Screen Only: If the top touch panel or aka glass top is cracked or broken but the image under it is fine, then you only need the Replacement Digitizer Screen for Nexus 5.
Complete Screen with Touch Panel and LCD: If the top touch panel for is broken and the LCD image is either black liquid or cracked you need a complete Nexus 5 Digitizer and LCD Screen Assembly.
The [http://www.etradesupply.com/lg/android-models/lg-nexus-5.html|Nexus 5 replacement parts] are for your reference.