As still a WP7 user myself, this is right up my alley!! And also, extremely easy as there are a number of ways to find apps:
1) Swipe left to the alphabetical listing of apps and functions. Scroll down to "Marketplace". Simply tap to launch, and the Windows Phone app selections will be there. You can browse by search (the magnifying glass icon), or swipe left to get to themes.
2) Launch "Bing", and type in the name of an app you are interested in (for instance, "ESPN"). The first search result will be any app that is available for your device. (In my example, "ESPN Scorecenter" will most likely show up, or "ESPN Hub".) Just tap to download.
3) You can also go to your "Zune" player and access the "Marketplace" option from the menu that shows up. It will then take you to the same page as the "Marketplace" option from your aphalbetical menu.
Hope this helps, any other question, do not hesitate to ask. The Arrive is a much loved and revered WP7 device. Hope you love it as well. That hardware keyboard is sorely missed by a ton of us in this day and age....