Can I use maps app in offline mode?

Not really, no. It buffers a portion of a map, but in general the Maps app, as with Google's map app, requires an Internet connection. If you need mapping when off line, look into one of the third-party apps that provide downloadable maps, such as the MotionX apps.

Regards.

Here's another source of mapping apps that work offline... http://bad-elf.com/pages/compatible-apps

Google Maps can now work offline as well but you must zoom to areas of interest and explicitly save your map data while connected to the internet. Use turn-by-turn navigation to get detailed (zoomed-in) map data, then search "ok maps" to save the data.