There are, to my knowledge, two ways to enable data transfer from an iPad to Garmin avionics. Both require Garmin Pilot, which automatically downloads all updates for your devices and transmits them over WiFi.
The first is a GI 275, which has built-in Bluetooth and WiFi capabilities. When the DB update is selected, it offers update via WiFi or USB. Once WiFi is selected, it briefly creates its own WiFi network, which the iPad automatically logs into (once set up) and the applicable DBs are transferred to the GI 275. Once the GI 275 has the updates, it propagates those updates to all other applicable devices (in my case, the other GI 275s and my GNX 375). Total time from selecting the update option in the GI 275 to all devices being updated is probably a minute. The only step requiring any intervention is the five seconds it takes to direct a DB update.
The second option is the Flight Stream 510. As others have noted above, which offers a similar capability to hardware which doesn't have WiFi built in.
For my money, it's hard to overstate the convenience of not having to screw around with Garmin DB manager on my PC, multiple SD cards, and keeping track of when updates are required. It's all automagical, requiring only that I direct a DB update when GP tells me there are new DBs available, or when my avionics grumpily inform me that they are not current. Haha!