I can't seem to symmetrize a smoothing function (see part in red attachment) with respect to the front plane.
What could be the cause of this problem please?
In addition, small "->" icons follow some of my functions/sketches in the creation process since I tried to make this symmetry. What does this symbol mean?
The -> means that you have an external reference. Would you have made a symerism in an assembly? In this case, you may have used a plane belonging to another part or assembly that generates this symbol.
If you are in a room to do symmetry, try to do a body symmetry instead and not a face or function symmetry. It's simpler. This is managed in the Symmetry function, you have to unwind the "Body to be symmetrical" moenu accessible only before validating the function. In your case, uncheck "Merge Volumes".
Edit: a bit long to answer, in line with my classmates! :)