Skill Pass gives you an opportunity to acquire additional Premium rewards in a Skill Shot.
While the Skill Shot lasts, you can purchase one Skill Pass which remains active until the end of the event. The Skill Pass will be activated the moment you purchase it and unlock the Premium rewards line.
You can purchase the Skill Pass in the Shop, or on the Skill Pass screen (Main menu - Events - Skill Shot), by hitting the Activate Skill Pass button.
Skill Pass provides the access to Premium line only. It doesn't provide unlimited Skill Shot entries. If you want to get unlimited free entries, you need to get the gold Subscription benefits.