Your data stays. Access drops to the Starter feature set until you subscribe.
During the trial you have the full product, including features that belong to the higher plans, so you can decide with real information rather than a feature list.
When the trial ends nothing is deleted. Your account drops to the Starter feature set, and anything that belongs to a higher plan is locked rather than removed: its records stay where they are and open again, exactly as you left them, when you subscribe.
You are not asked for a card to start the trial, and nothing charges automatically at the end of it.