Does Android support the external USB devices like PC keyboard, joystick, camera or other devices that can be connected to the PC? If so, then do I need some additional software, or is it enough to connect external device via Standard/Micro USB adapter?
All that depends on your device, which must support this as well. Android itself does support this since 3.1-honeycomb – and I e.g. successfully use an external keyboard with my tablets, which is just plugged into the USB port.
The keyword to look for is usb-on-the-go. We already have more than 60 posts on this topic, which you might wish to check (or start with the 9 most frequented to easier get to the core points). If those leave open questions, feel free to ask those in separate posts :)
Edit: As Dan correctly points out in his comment, if your device has a full-sized USB port, there's no need for OTG. See our usb-host-mode tag for that.