You should definitely know the term substrate if you've done enough research. Substrate is what you have covering the bottom of her tank. Wood chips? Shavings? Newspaper? Paper towel? And how thick/how many layers?

You definitely should NOT wait until you get paid to buy a thermometer/thermostat. You should have had it set up in her enclosure before even purchasing her. Heat mats are well known for overheating WAY too much & burning snake bellies. Look up pictures, it's awful & quite costly if they get an infection or secondary issue because of it.