Ok, first things first...
Find somewhere (front or back) where theres some soil you can get at, and that doesn't come from under a hedge or big shrub (which will have sucked up so much nutrient and water that it'll be powdery and won't give u a true picture. Then do the soil test as described. That'll tell you whether your soil tends to puddle & stay wet for ages, hold moisture nicely but not get boggy, or whether it drains so fast the plants havta sup up quick or miss it entirely. There are tonnes of plants for every type of soil, so u just need to work out what you've got and ur away.
The 'aspect' thing it just working out how much sun things will get in different parts of your garden. You can work this out with a compass, or just keep an eye out on a sunny day to see wots wot. You've prob got one mega sunny side, one thats pretty cool and shady most of the time, and 2 that are a bit of both. Deep shade in usually overhung by trees etc and looks dark like in thick woods. Light shade is out of direct sunshine but not actually overhung, so light levels are better. Partial shade in either shady more than half the time but sunny the rest, or that dapply light/shade u can get thru sparse trees. Partial sun is the reverse - like maybe 70% sunny, 30% shade. Full sun is when it really bakes. Again, different plants like or need different amounts of light, so once you know roughly what you have and where, u can choose stuff accordingly.
And pH. This is whether ur acid, neutral or alkaline. Some plants really care about this so u need to know. Easiest way is litmus paper (pinched from school) or a wee soil testing kit from garden centre. U only ever do it the once - once u know, u know.
And thats the basics. Wen u see a plant label it'll tell u - how much water in the soil, how much sun on its head and pH (if it has a strong preference).
So there u go. Maybe its worth finding a neighbour with a nice garden and asking them!!!