Light wooden framed structures were first created when some bright carpenters realised that the light partition walls they were putting up inside large heavy timber houses were capable of forming a construction system by themselves. The system was a skin made of timber members covered inside and out by sheeting.
This happened approximately a century ago. The process was accelerated by the widespread availability of cheap machine-made nails, and properly cut and planed pieces of wood produced by water-powered saw mills.
The american tradition of do-it-yourself also played a large role in popularizing this style of construction. Unlike heavy timber or brick masonry, wood framing does not require a special set of skills acquired after years of practice.
Equity is the difference between what your home is worth and how much you owe on it.
For example, if your home is worth $300,000 and you owe $100,000, you have $200,000 in equity. Over time, as you reduce the amount you owe on your home or the value of your home grows, your equity increases. It's that simple.