In order to add multiple terms and conditions, and/or exclusions to a proposal, you must first have them setup in the proposal settings.
In Step 3, and toward the bottom of the proposal details page, you will see the boxes for Terms and Conditions, as well as Exclusions.
Add one detail by clicking the + icon.
Once you've made your selection, you will tap the same + icon to choose a second detail from the dropdown menus.
Continue adding accordingly.
When you are finished, click next and finish the proposal as you normally would.