The options for subscribing can be found here https://fabrik.io/pricing.
You can subscribe to Fabrik whenever, before or after your trial end. If your trial does expire don't worry none of your work will not be lost, it will return to normal once you subscribe.
If you want to subscribe before your trial ends we still honour the trial period so the 14 days are always on us.
You should be notified when your trail is ending so you can upgrade from there. To upgrade you can click your name top right in the dashboard and go to manage account or just click this link https://app.fabrik.io/#/account/upgrade