First of all, you're absolutely doing the right thing in investigating this first, before you buy anything!
Definitely do that pH test as it will tell you a lot about whether you have chalk or peat. Also, just have a play with the soil. Water the ground and pick up a bit of dirt and roll it between your fingers. If it holds together, chances are you are on clay. If it feels really gritty and you can see quite large particles (like sand) you may well have a sandy soil. If you put a spade in and the soil tends to clump together rather than falling apart - also more likely to be clay.
The good news is that whatever you have, something can be done with it! Very few of us are lucky enough to be gardening on the perfect soil! There are only really a few places in the UK where you can put a spade in unimproved ground and find perfect loam. Most of us have to add quite a bit of organic matter on a regular basis. However, what you add depends a LOT on what you want to grow.
Say you find you have a sandy soil, for example. You could go in two directions: you could add loads of organic matter and plant things that like a reasonably free-draining soil. Or you could add rather less organic matter and do a dry garden. If you want to grow veg, whatever soil you have you'll probably want a big ole pile of well-rotted horse manure. If you don't want veg, though, too much horse manure can make flowering plants go very leafy instead of very flowery.
So basically, what you do with your soil depends a bit on what you have and a bit on what you want to do. But there are also some other factors to consider - and here's where it gets a tiny bit more complicated.
The first and most obvious one is weather. If it rains constantly where you are, then a dry garden is potentially going to be up against it. I'm in Sheffield, which is not exactly known for its hot, dry summers and the desert garden in the Botanic Gardens looks rubbish pretty much all summer. Of course, the same will be true if you plant shade-loving bog plants somewhere incredibly sunny and baked. Now there are people who relish this type of challenge - you always hear about those growing bananas and other exotics in the Pennines or tender plants in the north of Scotland - but you have to be a certain kind of person, with a certain amount of time on your hands, to make it work! It's generally easier and more rewarding to work with nature rather than against it. Particularly when you are just starting out!
The second one is your microclimate, and a big part of that is aspect. What way does your garden face? What kind of light do you get? Things like trees, structures that cast a shadow, slopes make an enormous difference here. I'm north-facing, but because the house next to mine is at an angle, I get a triangle of light during summer afternoons that enables me to part partial-shade things in that bit of the garden, with full shade things elsewhere. So have a look at where the light and shade fall at different times of day. Also, are there any problems with shelter: are you high up, windswept, or near the coast and liable to be challenged by sea breezes? These things are all part of the picture!
I realise this sounds complicated, but trust me - it's not. As you get to know your space more closely, it all starts to make sense. In the meantime, just try to observe really closely what's going on out there!