Here's the deal with cryptocurrencies.
When they are introduced or generated, there is x number of "coins" available.
That number of coins (at least with bitcoin*) is fixed. Forever. No new coins will ever be issued.
The bitcoin "wallet" is a digital repository of someone's coins. Access to that wallet requires a password, and that password was encouraged to be "secure", so not simple.
An unknown number of people can't remember their passwords, but it's thought to be quite a few; bitcoin was introduced years ago.
They bought bitcoin at $100 and probably have some in that wallet, but it is inaccessible and therefore can be considered removed from the market, probably forever.
Re-read the sentence about "no new coins ...".
So the amount of coins available to be traded/held is some number less than the introductory issue. This in itself will result in a natural increase in value per coin.
It is believed that something like 90+ % of all bitcoin ever issued is owned by about 10 entities. This creates a huge risk of currency manipulation, and also a huge risk of a "bubble" or collapse of the virtual currency.
The short answer is, if you are planning to invest, is to not risk money you can't afford to lose.
You can also earn bitcoin by processing the transactions. This is computer-intensive, but requires no monetary investment by you. It's debatable if the added cost of electricity from high heat / high activity processing is offset by the coin you will earn, but it's an option worth considering.
There are many advanced actors who probe and steal bitcoin wallets from computers connected to the internet. You need a secure system, and it's advisable to keep your bitcoin wallet offline. People losing / erasing /failure of a usb stick containing a wallet is another way bitcoin are removed from the pool, raising the individual value of coins, etc. Many transactions involving bitcoin require you to be online. So there is a problem there as well.
Many websites use or are infected with JavaScript that, unbenowst to you, are "mining" (processing transactions) bitcoin and some other cryptocurrencies. They are more common than many people understand, so it's practically guaranteed that you have probably been "hacked" (while that webpage is open or in the background but not closed) and have processed bitcoin for others, earning them money by stealing your electricity and CPU cycles.
That's probably enough for now. Hope that helps.
* There are new cryptocurrencies being introduced, I would consider them higher risk than bitcoin. This is classic patterns of "bubbles" and increases the risk of collapse some point in the future, at least for these less well established coins. YMMV