Resistance is essentially a 0-100% scale:
- 0% = no resistance
- 50% = half the max resistance (of the trainer capability)
- 100% = max resistance (of the trainer capability)
In reality, that is also impacted by your gearing, but essentially easy to understand like that. Here is a doc with more details.
Standard is a 0-9, and covered in the doc. Quite a few people really like the Standard option at 2 or 3, because the power curve is very “road like”.