how could methanol be extracted in leaves of plants? Like the crude methanolic extract.?

Methanol is water soluble so a extraction at room temperature ( no loss through evaporation) of leaves with water will do it. Unfortunately other components in the leaves are also water soluble, so you get an extract that must be refined. Filtration is fine for the first step and the second one should be a distillation from which you get a water/ methanol solution.