Ha, I bought my first (and only so far) SSD last year and did a little bit of research before. So if you don't mind, let me add a couple of things to what Pum said above.
SSDs
SSDs are still comparatively more expensive with respect to their price per storage unit ratio, £ per MB (or more correctly, MiBiByte). The reason for this being the technology implemented has its challenges for higher capacities (it's flash cell based instead of magnetic fields) which makes manufacturing them a bit pricier.
That's why these days HDDs are still pretty handy for mass storage. A usual case scenario for desktop PCs is the simultaneous use of SSDs and HDDs where the former is deployed as the OS running device and the latter for mass storage purposes (the way I use mine).
As different as the technology behind SSDs is, its advantage is indeed its notable faster speeds compared to their physical siblings (and all the other advantages Pum listed above). Peak performance for regular ones is around 500 to 600 MB/s. There are differences in performance and quality, though, depending on make/ model. The latest generation of SSDs are called NVME SSDs that are even numerous times faster than that (and hotter:)).
I bought a Western Digital Blue 250GB for about €40 for my 11 year old and only PC and I can tell you, it's pretty noticeable even when it can't even utilize its full potential due to old SATA II ports on my machine.
One thing you might have come across is the word TBW in connection with SSDs which could become a factor in your decision making process. In the past, SSDs came with a downside to them: Due to their flash cell based tech, they were more prone to fail over the course of their lifetime than traditional HDDs. The reason is flash cells can only be written and re-written a finite amount of times.
For modern SSDs this is practically a non-issue anymore due to their advanced technology. But flash cells are still flash cells that come with said limitations. That's why manufacturers these days advertise, in addition to their speed and capacity specs, an item called TBW which means 'terabytes written'. It tells you the amount of data that can be put through the storage device over the course of its life before the likelihood of potential write erros increases which then could cause your SSD to stop working properly.
To get an approximation of how long your SSD might serve you, you need to devide the TBW (in megabytes) by 365 and the amount of data per day you're expecting to be (re-) wrtiing to your SSD. For example, if you have one with 100 TBW (100,000 MB) and you expect to be roughly processing data to the extend of, say, 20 GB per day, your SSD could mathematically work for around 13 something years. Of course, your SSD might very well work beyond that (and most likely will). But given options to choose from within a selection of equal capacity SSDs, it would be better to get SSDs with larger TBWs just to lessen the risk of losing data. Samsung's EVO 860 series for instance states for its 250 GB model a value of 150 TBW which is one of the best I've seen so far (would equal 20 years of service in our above example).
Windows
Yes, changing your storage device, be it HDD or SSD, is no issue at all since they're not deemed crucial by Microsoft as identifiers of your machine. So, once you have activated your copy of Windows on your device, Windows knows it's yours (by creating a digital license) as long as you don't change crucial parts of your machine, e.g. your mainboard (which no one does with laptops anyways). Therefore, everytime you change your hard drive, Windows automatically activates your copy. When you change crucial parts, it's a bit trickier, also depending on where you live (e.g. USA vs. EU) because of different GTC.
One thing I've noticed with Win10 (due to involuntary re-installations of this damn OS) is that they want to force you into using an online account instead of a local one. In the past you had the opportunity to choose either but their latest version omitts that when connected to the internet and asks you to type in your Microsoft account instead. Since I had none, I tried to re-install it once again, this time without any internet connection, et voilá, I got straight to a local account (these assholes!!).
MS offers a tool called MediaCreationTool where you can download either an ISO file for a DVD or prepare a USB thumb drive to be used as an installation device. The latter will be your only option since optical devices are no longer built-in most of the time. USB is better anyways as it loads much much faster and you can update the thumb drive with newer versions anytime you like.
Laptop
Yeah, laptops. I don't like them that much. They're ok if you need to be mobil but they're also a pain in the ass. Especially the latest generation of consumer notebooks. Lots of them these days can't be really repaired or updated without troubles because almost everything is sealed. A while back, a friend of mine gave me his unused laptop and I simply wanted to remove the battery just to preserve it from being charged non-stop while working. I quickly realized that this wasn't possible because the battery was fully integrated. Nowadays, more and more the most you can do is change the storage device and RAM bars.
But what about you? What should YOUR laptop be capable of? What are you going to use it for? Just office work? Do you plan on watching movies and viewing pictures with it and hence need a good display? Price etc?
