Hi @Wendy,
Please see this thread for a previous discussion/answer to your first question about the FSC curve.
For your second question, the corrected FSC is calculated by applying the ..._mask_fsc_auto.mrc mask to the two raw half-maps (located in the ...map_half_A.mrc and ...map_half_B.mrc files).
As well, the volume_map.mrc is filtered by the “tight mask” FSC curve. The volume_map_sharp.mrc is the same as volume_map.mrc, but with one extra step of being sharpened to the estimated B-factor.
Best,
Michael