A CAS, or 'Confirmation of Acceptance for Studies', is required as part of the visa extension process.
If you are in the UK, you will complete a CAS application form during your short appointment with an International Experience Adviser. The adviser will then send the form to your college Academic Administrator. Allow a minimum of 2 weeks for production of the CAS.
If you are outside of the UK, the CAS will be sent to you once you have accepted your unconditional offer and paid your deposit. In some cases you may need a pre-CAS skype chat to determine whether a CAS can be issued. Or if you are a continuing student returning to continue your studies, your college Acadmic Administrator will send you a CAS request form to complete and return for the CAS to be produced