Pick one: Bitwarden (free, open source, audited), 1Password ($3/month, excellent family plan), or Apple Passwords (free, built into iPhone/Mac, no third-party needed). All three are excellent. The one you'll actually use is the best one.
Install the browser extension and the mobile app. This is the key step most people skip — if it's not in your browser and on your phone, you'll never build the habit.
On first setup, let it import everything from your browser's saved passwords. Every major password manager can do this. Now you have a starting inventory — probably terrifying — of every weak and reused password you have.
Sort by 'reused passwords' and fix your top 5 most important accounts first: email, bank, main social media, Apple/Google ID, anything financial. Generate new unique passwords for each. The manager remembers them. You don't have to.
After that, fix passwords as you log into sites naturally. Over 2-3 weeks, every account gets a unique strong password without a dedicated session of misery. Set up emergency access so a trusted family member can get into your vault if something happens to you.