You are required to fill the domain authorization code. It can be obtained from the domain current registrar.
Upon initiation of the transfer, an authorization code will be sent to the domain admin for approval. The domain admin needs to response to the transfer within 5 days from the initiation date. If there is no response from the domain admin within 5 days, the transfer will be cancelled automatically.
The whole transfer process will take 2-10 days to complete, and the domain will be renewed for one year upon completion of transfer.