An estimate goes through a number of stages in your workflow after having been created. When an estimate is first created, it will default to the status 'ongoing'. Once it has been filled out and actually sent out to the customer, this status will change to 'waiting for the customer'. From here, the status will either change to 'rejected' or 'accepted' appropriately based on what takes place next.
As an example, filtering your report to show all jobs in the 'ongoing' status will show you all the estimates that have been raised but have yet to be sent to the customer. Filtering for the status 'waiting for customer' will show you any jobs where the estimate has been raised and sent but has yet to receive a response.
You cannot filter by more than one status at a time but you can create multiple reports if you wish to view different statuses simultaneously. Please note that if you book an appointment in after you've sent the estimate to the customer, it will change the status back to ongoing.