Understanding the type of knots that are allowed to be opened on Shabbos.
ודבר דבר (Dabair Davar): Is One Allowed to Talk About Other Things That Are Not Allowed on Other ימים טובים (Yamim Tovim), for Example,...
shailos with mixing red and white wine; mixing tea essence with hot water;
How to Deal With Putting Items Into the Refrigerator, for Example Sodas, That One Will Need for מוצאי שבת (Motzei Shabbos);