There are two ways to add a selection item. To add a selection item just to one project, click the + New option at the top of the Estimate or Specs & Selections page. Choose Selection from the list of options.
If you have selection items that you will reuse from project to project (even if the exact prices or other details may change), you can add them to your Specs & Selections Templates to make your life easier. You can access the template library from your top navigation. Once you have added items to your template, you can copy them over to a project by clicking the + New and choose Copy from Template on the Estimate or Specs & Selections page.