Then go to Tools > Board > Board Manager:
IDE Board Manager
Type ESP32 and Install the new hardware libraries:
ESP32, a low-cost and extremely versatile microcontroller with integrated WiFi and Bluetooth.
Useful link TTGO WiFi external links: ESP IDF Adruino ESP32 Libraries
Very helpful external site https://randomnerdtutorials.com/esp32-pinout-reference-gpios/
Complete microcontroller with WLAN (802.11bgn) and Bluetooth (Classic and LE).
Reset and boot buttons are available, so a new firmware can be quickly and easily installed.
The ESP32 combines a CPU with 2 Tensilica LX6 cores, clocked at up to 240 MHz, and 512 kilobytes SRAM in a single microcontroller chip.
If you want a very good version with a small colour display checkout TTGO T-Display
To add ESP32 to the Arduino IDE software paste the following line into the Additional Boards Manager URL:
https://dl.espressif.com/dl/package_esp32_index.json
Introduction into ESP32 with first tests: PWM, Servo, Web, Touch Sensors (Tutorial)
Testing the Heltec ESP32 with the Onboard OLED
https://robotzero.one/heltec-wifi-kit-32/
Using the second core see Dual Core
Using Bluetooth
ESP32 Bluetooth BLE with Arduino IDE
NOTE the very cheap ESP32-C should be available in early 2021, Comes with increase in memory to 400KB SRAM and 384KB ROM and a RISC-V processor but clocked at only 160MHz.
ESP32 Deep Sleep Ultra Low Power Coprocessor
Audio