Once you get use to it, it's actually pretty simple (except entering addresses). I've had the same issue with the GPS, it seems that it takes a while in this app to get it started. I've found two things that work though. To get the GPS working right away when you open the app, I would suggest that you open up the native Maps app (Google maps) and let it locate you. Once the blue dot blinks for a couple seconds, you can exit out and start G-Map. That way when you go to map in G-Map, it will locate you immediately.
The other option if you're driving somewhere, is just to enter the destination and let it calculate the route. It usually takes a 1-3 minutes for the app to find your location while driving, and when it does, it re-routes to give you the right directions in real time. Anyhow, that's what I've found works for me most of the time. Make sure that the phone is close to the windshield, it works best that way.
Entering an address is such a pain, I wish they could just do what Google maps does, and I wish they could pull up addresses from your contacts. When entering an address like for example "1234 SW Broadway," you first have to enter and select "SW Broadway," and then you have to type in "1234." Then you have to select "1234 SW Broadway," and click the Go button.
Hope this helps. Oh yeah, and always select the autolock to never, before using the app, so the display doesn't turn off on you.