After you save your ladder you will be taken to its manage page. While your ladder is in draft, activists will not enter it. From the page you can edit or publish the ladder to make it live.
You can also test the ladder from the manage page. Enter an email address in the testing section and choose a trigger and submit the form to begin your test. That activist will enter the ladder as if they had triggered that trigger and move through in the way they would as if the ladder was active, moving from step to step, receiving email, being evaluated by decisions based on their current user record, and the like. Wait steps are truncated to two minutes to enable expedient testing. It is recommended you create fake activists with email addresses you control to test ladders. You can manipulate the data in their activist record to enable you to test various portions of your ladder and the paths an activist might take as they move through it.