Hi,
Wifi Router comes with USB connection to provide internet connectivity to your computer through USB port. This may be DSL modem with wired internet input.
3G dongle with USB port need to be connected to laptop directly to get internet connectivity through USB port. Here USB port also powers the dongle and get internet signal from the dongle. But dongle can provide internet connectivity to only one computer and no wifi available.
Now you can connect this dongle to a Wifi router which has USB input to insert dongle and probably another micro-USB input for charging purpose. This may give out the signal either as Wifi (wireless) or through ethernet port for wired connectivity to your computer. Here you need to buy extra hardware - Wifi router for USB dongle
Alternately you may buy Wifi dongle, which also have USB connectivity. They may either be directly connected to laptop like any other dongle, or alternately they may be connected to any powerbank or charger to get power through USB. Since such Wifi dongle may not have power source, power required to be fed externally through charger or powerbank. USB charger or power bank will be extra hardware. Otherwise you must be having a device like laptop which can power your Wifi dongle