+1 to the advice above but I notice you asked about which sides of the strop to use. After the cloth/nylon you strop on the smooth side of the leather. Also it is a good practice to place the strop flat on a table or something and rub it with the palm of your hand about 100 times. This will transfer some of your natural skin oil into the strop and that done quite frequently will condition and maintain the leather. When it comes to pastes, they are applied to the rough side of the leather but as said previously you need not worry about that just yet.
Good luck and enjoy your new hobby.