The chips work similar to the Arduino Uno with a some limitations. I found that advice on the web was sometimes confusing or in a few cases wrong. You are left to figure the rest out on your own.
I put together details on some aspects. I hope you find there is enough detail to make using a ‘tiny easy.
When you use an ATtiny84 or ATtiny85, you are most likely using a breadboard or circuit of your own design. Unlike an Arduino Uno, that has the pins at the headers numbered to match the pin numbers in the Arduino IDE, you will have to wire your ‘tiny to the actual physical pins.
The physical pins and the pin numbers in the software are very different. For example, on an ATtiny84, physical pin 1 is for Vcc while, in the software, digital pin 1 is actually physical pin 12. You have to understand from context which pin (physical or software) is being talked about (hint, most references are for the software pin). It is best to refer to a diagram as you go through the explanation.
To add more confusion, the analog pins can have different numbers than the digital pins at the same physical location. This is happens with the ATtiny85. For example, the physical pin 7 is both the digital pin 2 and the analog pin 1. Digital pin 1 is the physical pin 6, and it has no analog input. (I only hope that the chip designers saved the company a lot of money for the confusion this can cause.)
This situation is due to the chip designers and not caused by the Arduino software. The pin numbers are based on how port B and the ADC is mapped. Pin 7 is PB2 (digital pin 2) and ADC1 (analog pin 1).