Whether or not you need to confirm a booking depends on whether you've made a direct booking request or posted a job.
Direct Booking Request
If you've sent a direct booking request to a carer then there there is nothing else to do to confirm your booking. If the carer accepts the request then your booking will be confirmed.
If you've posted a job, then once you've received applicants you will need to hire one in order to confirm the booking. To do this, you can view your booking in the app or website and then select "Hire" next to the carer you wish to confirm. One you hire an applicant, your booking is confirmed.