IMO, best medium to start with is earth. So, soil, I guess, but not bagged soil.
Firstly to get to know the look of decent soil, that will hook one on the composition of the soil and from there you take it step by step. Some bagged soils may look and smell amazing and is adverized as the best thing under the sun and this can really be discouraging to some as most comercial soils do more harm than good when it comes to growing cannabis.
Understanding the whole picture, instead of building an interest around one thing and seeing that as the holy grail and only thing that works, just because it makes more sense to you.
More importantly, WHEN is the best time to START? Honestly, few years ago. Second best time is RIGHT NOW.