There are many ways:
1. Faucets, giveaways, and other "free" coins. This is how I started. I guess I filled more captchas, than I should.
2. Buy them. This is how I got >90% of my coins.
3. Earn them. Well, some time ago I agreed to wear a paid signature.
4. Mine them. Not directly, but by mining and selling altcoins. Maybe in the future, it would be possible to directly mine millisatoshis (or even smaller units) on my CPU, and to contribute to the total hashrate, by putting a single drop in the ocean of miners.
5. Gamble them. Sure, I also did that. I got something around 1% of all my coins through gambling, but I guess it is mostly connected to faucets and giveaways. However, gambling is also a nice way of changing your coin amounts, if you need that, and rounding it up or down, depending if you win or lose. Usually, I gamble something around a transaction fee, and get either a "free" transaction, when my fees are paid by casinos, or "2x fee", if I lose.
6. Employment. I thought about it, and even tried it sometimes, but it is hard, to get it right. I am still far away from leaving my current job, paid in fiat, or from being paid directly in BTC. Maybe in the future.
7. Puzzles. There are addresses with very weak keys (for example private key equal to one). There are coins, signed with SIGHASH_NONE. Many coins are flying around, and sometimes you can even get them, without any signatures:
https://mempool.space/address/bc1qft5p2uhsdcdc3l2ua4ap5qqfg4pjaqlp250x7us7a8qqhrxrxfsq2gp3gpSo, I guess if I bought most of my coins, then this is what I should tick in the poll.