/r/saplings is a subreddit dedicated to first timers and newbies to cannabis. It has every answer to your questions and will be happy to help beyond that.

To answer a few of questions to the best of my ability though..

First time experiences vary, obviously you want to start small and work your way up. Alot of people (including myself) didn't really "get high" the first time I tried it, and it wasn't until the second time I smoked did I really get the sensation that is considered "being high".

You mentioned you have Asthma, and being the first time smoking the hits are going to feel extra harsh. I would recommend vaporizing over smoking but purchasing/locating a vaporizer can be somewhat difficult/costly especially since it's your first time smoking..

When it comes to buying weed...

Well basically you have 2 strains/types of weed - Cannabis Indica and Cannabis Sativa. Indicas give you a more relaxing, sleepy, painkilling, body type of high whereas Sativas give you a more uplifting, energetic, mind type of high. (This is due to different levels present in each strain)

Depending on your dealer/location it can be quite hard determining what type of weed your dealer has. Australia is way behind the ball compared to the USA and alot of people here are just happy buying "weed" sativa/indica they don't care.

I've found that Australia has alot of Indica dominant strains, and quality varies alot. Although you can find hobbyists and some pretty professional growers out there that really know their art, and you CAN get product from them that compares to the shit in the states.

just my 2c but definitely go check out /r/saplings