Wiring SMD Micro USB to ESP32 MCU
Most of these USB to UART devices has ability to operate a variety of features for RS232 systems. They are used to send signals or receive signals back from devices for proper operation.
You wont need them if you are using it to program a ESP32 module. For that, you will only need RX(Receive Data), TX(Transmit Data), RTS(Request to Send), DTR(Data Terminal Ready), D+ and D-.
Answering your second question, that is to put the device in Flash mode. IO0 and RST pin of the ESPs need to be in a specific state for that operation. When you press the Upload button in our IDE, the IDE will send a command though D+ and D- which will tell the UART device to send signals to the MOSFETs in that schema. This will set RST and IO0 to LOW and they will be set back to HIGH in a synchronized manner. This is to enable the device to go in flash mode without the need to the user to press any button.