There is no such thing as a free AWS account. However, there is a free usage tier that provides a certain amount of select services at no charge, typically for the first 12 months of the account.
The free usage tier does include 30GB of EBS storage. This means that the first 30GB of EBS storage for an entire month is free every month. This could be used as 60GB for half a month, 120GB for a quarter of a month or 30GB for the whole month. This logic applies to all services -- AWS services are typically calculated on an hourly basis, so the hours can be used in parallel if desired.