This is a process which cooks pastry prior to adding the filling. If you add pastry to uncooked pastry it often won’t cook.
Take a square of chosen paper (greaseproof or parchment), which is bigger than the tin you are lining. Fold it in half, then in quarter (so you have a square again). Keeping the middle point , fold again and again, you should have a sort of V shape. Hold this over your tin. Tear off the wide end so it is just slightly larger than you tin. You should have a circle. Scrunch the paper so it lines the pastry. Place some dried beans, lentils or rice on top of the greaseproof or parchment paper circle, fill to top of tin. Place in oven. After about 10 – 15 minutes the pastry should look set. Remove cartouche and prick bottom. return to oven until pastry looks a light golden colour and cooked through.