Does Android support the external USB devices? 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.