The ATTiny85 is an Atmel AVR board that is a small in form. It is like the little brother to that ATmega32p that is found in the Arduino boards. It has all the same kind of functions but with fewer GPIO pins.

• Official product page: https://www.microchip.com/wwwproducts/en/ATtiny85

SparkFun has a nice pinout diagram: https://learn.sparkfun.com/tutorials/tiny-avr-programmer-hookup-guide/attiny85-use-hints

SparkFun also has a nice one-page PDF reference guide for ATtiny85: https://cdn.sparkfun.com/assets/2/8/b/a/a/Tiny_QuickRef_v2_2.pdf

The `o` represents the circle indentation in the board.
Align the `o` to the top-left where pin 1 is.

 Reset  1 -o==- 8  5V
 A3/D3  2 -   - 7  D2/A1 (SCK)
 A2/D4  3 -   - 6  D1 (PWM, MISO)
 GND    4 -===- 5  D0 (PWM, MOSI, AREF)

Use an Arduino UNO as ISP to program the ATtiny85.

Wire up the Arduino UNO to the ATtiny85 over GPIO pins. Add a 10uF capacitor between RESET and GND in the Uno (anode to ground) to prevent the upload causing the board to reboot.

    Uno:ATtiny85
=======:========
     5V:Gcc
    GND:GND
 Pin 13:Pin 2
 Pin 12:Pin 1
 Pin 11:Pin 0
 Pin 10:RESET