Fibre optic Internet connection lines use a different type of technology to transfer data too and from the Internet than regular coaxial connection lines. Because of this, you can't connect a fibre optic line directly to your Ethernet switch. Instead, you have to connect your fibre optic modem to the Ethernet switch using an Ethernet cable. The modem will convert the information from a fibre optic signal to a signal that can be transferred via Ethernet cable, at which point it will then be passed along to the switch as normal.
Connect an Ethernet cable to the Ethernet "Out" plug on the back of your fibre optic Internet modem. On most regular modems (units that do not also act as routers), there will only be one Ethernet plug on the case. This is to be used for connecting the Ethernet cable. This plug will also likely be labelled "Out," but this may change depending on your model.
Locate the appropriate Ethernet "IN" plug on the back of your Ethernet switch; some of the plugs are available to connect computers to the switch, while one plug in particular is made to connect the switch to the Internet. Locate the plug used to connect the switch itself to the Internet. This plug will likely be labelled "In," but this language may change depending on which model you have. This plug will also be in a different area of your Ethernet switch's case than the ones used to connect the switch to other computers. If you need help, consult the diagram of the various plugs in the manual that came with your specific model of switch.
Connect your Ethernet cable to the Ethernet "IN" plug you located in "Step 2." Your fibre optic line will now be connected to the Ethernet switch.