I bought an Arduino UNO R3 Yesterday. It's a Chinese clone. But it has the Atmega328p and MEGA16U2 both. I've installed the IDE fully. But it can't find the ports. The Tools > Ports option is greyd out, Cannot find The options Named "Ports (COM & LPT)" or "Other Devices" in device manager. Can't upload any sketch to board. I tried this on my both Win7 SP1(32 BIT) & Win10, which are installed in the same pc but in different partitions. I've roamed accross stackexchange but no successful result.
You may not have installed the drivers when installing the IDE. The only way I know to reinstall the drivers is to reinstall the IDE and make sure when you get to this screen you tick every box:
Otherwise you may not have selected your board correctly. To select your board in the IDE, go to Tools > Board > Arduino Uno/Genuino Uno
Your port select may then appear, it should be COM1 or something similar. If you have multiple, just try them all by selecting one and then upload a sketch to it. The Arduino Uno should flash some lights if it worked correctly.