Use Depth of Field to create a blur that is applied to out-of-focus points of light to simulate a shallow focus.
To access the Depth of Field menu, use:
Batch, then select a node from the Node bin.
Timeline, then use Batch FX (see Creating Batch FX).
Tools, then select from the menu (See Accessing Tools).
This node accepts a front, Z-depth and matte clip, and outputs a result, out Z-depth and outmatte clip. The output matte clip can have a different level of depth of field than the result clip.