For someone starting with zero experience in DAR.

If you're on PC, use Leth's Ice Rings and set the game speed to 70-80% (whatever you're comfortable with).

Hold directional air roll while your nose is pointed straight up and feather boost to go through the rings whenever your hood is facing you (since left is left, right is right, etc).

Do this for 15 minutes, twice a day, for 3 weeks.

Levels 1-3 should take about a day or two if you're consistent.

Level 4 should take about 3-4 days to able to do consistently.

Levels 5-6 should take about 2-3 days.

Level 7 might take up to a week due to the vertical climb and camera reorientation.

Remember, the above is based on 15 minute intervals (2x a day).

Once you can comfortable complete level 7, the movements should have clicked enough where Levels 1-6 can be done within a few minutes.

Now it's just repeating the same thing over and over for a few months. By months 2-3 you should feel fairly comfortable using it in game for aerials. Every now and then you can hop into an aerial training pack and try to hit the ball while constantly air rolling.