Are you talking soil as in directly from the GROUND? Or a soil-mix that has been amended and designated for container gardening?
A hell of a lot goes on within soil indoors and out, but soil from the outdoors typically isn't suitable for container gardening for various reasons. Among these is a potential for poor drainage and the soil becoming waterlogged; but there are also various species of micro-organisms dwelling in the soil (bacteria, fungi, protozoa), along with microscopic worm-like creatures known as nematodes, as well as a plethora of insects and bugs (arthropods)-most of which you'd have to focus on carefully to see with the naked eye.
In nature everything happening among these living organisms typically boils down to an equilibrium: a distinct balance. Many species of bacteria, fungi and protozoans are strictly beneficial. We really
want them to be in our soil because they do good things for it and for the plant. Even many nematodes and arthropods are beneficial and desirable as they not only consume pest eggs, larvae and bad fungus and bacteria- but also excrete wastes that fertilize the plant and continuously mix and aerate the soil. When you take soil from the outdoors and put it into a container- aside from having no idea which kinds of detrimental microbes and other pests might be present, you can't be sure the good ones are there in healthy populations either. The favor tilts in the direction of the 'bad', detrimental microbes and organisms. You could bake your soil to sterilize it, which would kill
everything in it but that still leaves the other issues to consider.
As for nutrients, organic soils may be loaded with amendments that fertilize. It is nice to know exactly what is in your soil so you know if you need to add anything immediately or not. You can always do a soil test (with the colored capsules) to at least check the NPK levels. You can amend your soil with things like earthworm castings, steamed bone meal, guano, kelp etc. before you plant into it. Certain organic fertilizers may become available to the plant over the course of several months, even years, while others are quite available immediately. Organics depends on microbes and organisms to decompose organic matter into humus, fix and mineralize nutrients. This doesn't always take ages, as bacteria can work quite quickly and efficiently.
You can do a simple test to check the drainage of the soil you acquired: put enough of it into a pot with drainage holes, pack it firmly and water it. Note what happens; if it becomes muddy/mucky, compressed or if the water puddles and doesn't drain promptly (within a minute) I definitely wouldn't use it. Amendments like coco coir, sphagnum peat moss, perlite, pumice, humus, and vermiculite are used to improve soil structure and drainage.
This is an awesome overview of the soil food web that will allow you to become familiar with what goes on within living soil:
http://soils.usda.gov/sqi/concepts/soil_biology/biology.html