Your variables can be viewed in the "Variables" window (under "Project Design"). You can view them in a grid view (default) or table view - to change between views, click the grid/table icon at the upper right part of the window (beneath the "+ New" button).
Reorder variables
The order of your variables can be changed in both views. Drag and drop the variables in your preferred order. The variables will appear in the same order in the dataset window and when adding new entries (unless defined otherwise in a form).