There are sensors in the stores that send/recieve a signal. So when you walk in just hang out at the entrance for a couple of seconds and watch for it to pop up on screen. And at stores such as Best Buy, there a sensors in the gaming area and/or digital imaging area pending what and when they are active. So you just walk over to that area and get those "walk-ins" as well. Walk-ins don't seem to be limited at this time. You can collect them everyday as opposed to scanning products which are limited to 1 to 5 times every 30 days.
The ink bonus that you mention is a scan. Scan points are acquired by scannig the UPC symbol of the product featured.
As you say, its a pretty simple app. Can be monotonous at times pending your pursuance of points but with easy rewards.
At the top of the screen there is a bar under the kick points counter. That yellow part shows your advancement towards the next level. Everytime you pop open, or browse as they call it, a store you get a level point. You'll see a glow surround the level bar when you "browse" a store which siginifies you earning a level point. The higher the level you are, the more points you can earn just by "browsing" and more bonuses become available.
*edit
Also, if you tap on your points total at the top of the screen, it will blow up to fill the screen and show you your level credits and the total needed to get to the next level.