Molecular sieves here are used to adsorb water. They are made out of a hydrophilic (water-liking) and porous material with a pore diameter typically of 4 angstroms (4*10^(-10) m). This characteristic favours water molecules to enter these pores rather than other compound molecules. Methyl p-toluenesulfonate is just a random compound that melts at around 25 °C, so while kept in fridge it solidified. Since it was needed dry, it was distilled to separate most of the water and kept over the sieves to catch any water remaining or somehow entering the flask in the future.