Select one of the Output nodes PICT Export, TIFF Export or JPEG Export and define the location of the exported files. PICT is faster, but TIFF allows for saving a mask. For JPEG, you can set the compression quality. Select Render All or define a range of images to render.
Now choose the menu command Render to render the selected output nodes or Render All to Render All output nodes.
Note: You always render at the current resolution.
Note: You can always stop a rendering by pressing on the stop button, by pressing command-period or escape. Note that the current frame will still be exported.