The hryvnia is issued by the National Bank of Ukraine, which also sets the rules of its circulation. Bitcoin has no issuer at all: new coins appear on a schedule fixed in advance and carried out by the network itself.
A key instead of a document
Your rights to the funds are proven by a private key, a long string held by your wallet. Nowhere in the network is there a record saying "this account belongs to so and so". Hence the main consequence: a lost key means lost funds, and there is nobody to restore them.
Different things under one word
The word cryptocurrency covers both bitcoin and ether, whose prices float freely, and stablecoins pegged to the dollar. For exchanging they are different tasks: in the first case timing matters, in the second it barely does.
Where the price comes from
Only from what buyers and sellers agree on. No state and no company revenue stands behind a cryptocurrency; demand alone sets the price. Hence both the scale of the swings and the fact that there is no "fair" price here.
What to do before your first purchase
Set up your own wallet and understand where the seed phrase is kept. Funds on an exchange are yours in name only: the platform controls the keys.
And check how you will get back into hryvnia. Buying is easier than selling, and the way out is worth knowing in advance, along with its fees and its timings.
Read more: Where to start and what not to do