How do I add a field to a PowerApps form?
On the Properties tab of the right-hand pane, select Edit fields. In the Fields pane, select Add field, select the check box for each field, and then select Add. Select the ellipsis (...) next to Add field, select Collapse all, and then drag Name to the top of the list.
How do I add more fields to gallery in PowerApps?
You do this by selecting the gallery (either on the canvas or from the left menu) and then clicking "Edit" - see below screen shot. From here you can add fields. If you want to display these fields in your result/gallery you mark the first item in the gallery and click "Insert" on the top ribbon and select "Label".