First of all, there's no reason to be scared about asthma. If you do right, it's pretty controllable. The numbers are "peak flow". You blow in a tube with a gauge on it and the strength of your breath is measured by how far up the scale your breath pushed the gauge. Depending on your score (if it is low), then they will give you a bronchial dialator and retest you to see it it helped.
It isn't painful, no needles, no tunnels, just blowing till you can't get another wisp of air out. So, practice taking BIG DEEP breaths and blowing out till you've expelled ALL the air from your lungs. It'll help.