Just query directly.
2) 2) The resistance between P0 port and LED is "pull-up resistance", which is used to improve the port driving ability of single chip microcomputer. If you don't add a pull resistor, even if the port is set to 1 (high level), the LED won't light up, because the MCU port can't output such a large current, although the LED doesn't need a large current.
3) The circuit at the 3)RST end plays a reset role. Press the key, and the MCU program starts running again.
4) that EA port is the enable end of the external memory of the singlechip, and when EA is connected to a low level, the singlechip read the data of the external memory; When EA is connected to high level (that is, connected to power supply), the single chip microcomputer does not recognize the external memory.
5)XTAL 1 and XTAL2 are connected by a clock circuit, and the core device is a crystal oscillator, which provides a pulse signal with a constant frequency (generally 1 1.0592MHz) for the single chip microcomputer, and each pulse is equivalent to a heartbeat, so that the program instruction of the single chip microcomputer is executed a little earlier.