It will be easier to give you advice if you can state what the journey for the season ticket will be, as this will affect the options available.
I think from the OP's post this will be a member of TfL staff wanting an annual season for travel on National Rail services to London. Which is why the journey details are key to how to proceed.
Ah yes I thought new to TfL as in not travelled in London before not new as in just joined as staff.
That is also a possibility, of course.
You're asking for advice, but you're not giving us the information we need to give it.
Alternatively you can purchase on the southeastern trains website and have the ticket added to their smart card
ticket.southeasternrailway.co.uk
Please be clear, are you a TfL employee, as suggested by your comment that "I am new to TfL"? And where in London do you need to travel to? Is the form you completed just to get the season ticket loan or to allow you to purchase a discounted season ticket?
Thanks. You can order a Key smartcard online from Southeastern, or a smartcard from any other train company. If you have the Southeastern smartcard you will also need to carry separate photgraphic ID when you are using the smartcard. If you obtain a smartcard from a train company such as LNER you can order online and have the smartcard provided with a photo on it which avoids the need for a separate ID. You can then buy the season ticket at a station or online but if buying online many train companies restrict the issue of seasons to smartcards they have issued themselves. Sorry this all sounds a bit confusing!