Creating an AWS account is free. But using its services will cost you. But AWS provides a free tier account for any new user for a 12 month period.
Now in the free tier account, you can use services for free up to a limit. As you have asked about 30GB storage which I guess is EBS and instance in the case an EC2 server which is t2.micro (free tier eligible).
Pointers to remember about the AWS free tier:
- After the limit per service, you will be billed
- For EBS, every month you get 30GB storage for free but you can create a 100GB EBS volume and not store anything in it or store lesser than 30 GB (you won't get charged)
- You can launch any number of EC2 t2.micro instances, but their combined running time should be equal to or lesser than 750 hours/month. Only then you won't be billed, if you use a different instance type or go over the monthly limit, you will get billed.