This question already has an answer here:
Lots of spoilers, obviously.
At the end of the last series, in The Name of the Doctor:
The Doctor and Clara are forced to travel to Trenzalore by the Great Intelligence, where Clara steps into the Doctor's grave - a scar in spacetime where she is scattered across his history. The 11th Doctor jumps in to save her and it ends on a cliffhanger where they meet the War Doctor for the first time.
Then in the 50th anniversary special The Day of the Doctor:
It starts with Clara working as a teacher and the Doctor travelling.
How? What happened between these two episodes? The 11th Doctor mentions Clara having met 'Mr Grumpy' before, but there seems to be some missing narrative. Have I missed a special or something?
How do Clara and the Doctor escape from the Doctor's grave on Trenzalore?