When logging in or signing up for a new Gravit account, everybody is entering into the trial version of Gravit Designer PRO. This allows you to try all the PRO features for 15 days. You can see how many days are left in your trial in the yellow countdown banner on the bottom-right.
After the trial is over, Gravit Designer automatically changes to the free version. The PRO features are not available in the free version of Gravit Designer. Please check the comparison table here. You can use Gravit Designer for as long as you want without any costs but if you want to keep using the PRO features after the trial expires, you need to buy a subscription.