It'll be in all the emails. When you received this email, it meant that you're in the PGDE Program. And under this PGDE, you'll first need to do a contract teaching with your contract school. The details of your contract school will be out 1 week before reporting date. During this period, you're doing contract teaching. You'll have the duties as a regular teacher, just that you are untrained.
Key personnels (VP/P) will have to assess you on classroom management maybe at the 3rd or 4th month. I did mine on the 3rd month, this is the formal observation where they'll decide if you are suitable for teaching. If you are, then they will write in to NIE to recommend you to undergo the 16 month PGDE training. If you're not, then they might give you another chance or extend your contract.
Hope this helps