For a 2 column from you need to make sure the CSS Design you have selected is set to create a 2 column layout.
In the Form builder wizard click the customize CSS button, set the width of the form, and set the columns to 2, set the width of the columns to be half the width of the form.
now when adding elements to the form, you will first add the group, go into the edit group screen, each group will be made up of Lines. each line will have Set 1 and Set 2, items in Set one, will be in one column, items in set 2 will be in another.
For an example, you should examine the brassy design, this is a 2 column design.
for the tab order, you will need to set the tab index for each element after the form is created.