When your trial ends - 30 days or $5, whichever comes first - your services are stopped until you either upgrade to the Free plan or to one of the paid plans (Hobby and Pro)

Is the free plan the $1 credit plan? And do i have to switch manually?

Yes and yes, when your trial is over you can go to https://railway.com/workspace/plans and scroll down until you see the option to upgrade to the Free plan

Thank you