It looks like you started our 7 day trial. This is simply 7 days of Premium 100% free and you will not be charged for it.
Once your 7 days of Premium runs out your account will return to the 'Free' status.
If you decide you want to try out Premium for a bit longer then you can always grab our 30 day Premium trial. Just be aware that the 30 day trial does turn into a subscription after 30 days so you will be charged after 30 days is up unless you decide to cancel it before it runs out.