The SG100-24 is unmanaged, so the options that you have for high-speed aggregate connections that you would have on the higher-end units aren't there. The best thing is to just use one of the copper gigabit ports on each of the switches to connect them together and then connect the router on another port. Using the SFP interfaces doesn't make sense because the switches are physically close to each other and so there's no advantage to using a fibre connection.
