Methanolic solution is defined as a solution that contains methanol used as a solvent. Therefore I think that this solution can be used as a co_solvent for the synthesis reaction of schiff bases.
About how to prepare it, you can read material as follows
As Dang said. Its just methanol. In general, Schiff bases are synthesize in methanol or ethanol, sometimes with an acid catalyst (like a drop of formic acid).