You can search for Marketplace applications in several different ways.
From the AppGallery home page:
Search by industry:
Click on an Industry in the list.
Search by device:
Click on the drop down menu next to "All Devices".
Select a device in the list.
Search by app name
In the Search field, enter the app name and press the Enter.
You can also search using a combination of industry, device, and/or app name.
You can also clear your search by clicking on the Home button on the left top of the screen.