Task fMRI voxel-to-voxel analysis

Dear all,

I am analyzing some task fMRI data and I would need your expertise regarding the analyses.
I have a paradigm containing a mental task and a control task. I also have two groups: patients and healthy controls.
Until now, I have done all the preprocessing + the first level analyses (voxel-to-voxel analysis), but I don't see how I can do my second level analysis.
My goal is to get the difference in activation between the two conditions (mental and control) in each group and to compare this activation between the two groups (patients and healthy controls).

Your help would be much appreciated,

Thank you,

Ismail