A bull market is a sustained period of rising prices and optimism; a bear market is a prolonged downturn marked by falling prices and caution. Crypto cycles between them, often more sharply than traditional markets.
The danger for beginners is emotional: bull markets create FOMO (buying tops out of fear of missing out), and bear markets create panic-selling at lows. Both tend to lock in the worst prices.
You can't reliably time the switch between them, so the steadier approach is a plan you stick to in both — for example, dollar-cost averaging and only investing what you can afford to lose. Cycles are normal; reacting emotionally to each one is the costly part. This is educational information, not financial advice.