Arduino Uno + KTY81/210 temperature sensor

Hi,

Sorry, I am new to this and am unsure about a lot of things, so I need clarification. I haven't found information that explains how and why things work, only "do this, do that"

I am following this guide (arduino-thermistor-temperature-sensor-tutorial) to connect a thermistor to my Arduino Uno.

Here is my temperature sensor information:

Temp. Sensor 2000R +-1% TO92
Part.No.: KTY81-210
Name: Temp. Sensor 2000R +-1% TO92
Description: 2.5mm, 1980...2020Ohm, -55...+150°C

And here is the sensor's data-sheet: sensor data-sheet

I have connected everything the same way as in the guide. Everything works and values are being serial printed.

What I don't understand:

1. The thermistor's and resistor's Ohm value should be equal, correct? In this case 2000 Ohm?
2. My thermistor has a PTC, so I'm guessing I have to invert the math or use an NTC thermistor instead to get the correct values? (currently as resistance goes up temperature goes down)
3. As I understand the code uses the Steinhart-Hart math logic to convert resistor value to temperature value, so I need the A, B and C coefficients of my thermistor for the equation. I don't understand how to get them from the data-sheet. Do I just take three temperature and their corresponding resistance values, put them in a calculator and use the resulting coefficients?