If you only change one thing about your online security this year, make it this. Reused passwords are how most accounts get taken over, and a password manager is the only realistic way to stop reusing them.
How it works
You create one strong master password. The manager encrypts your other passwords with it on your own device, then syncs the encrypted vault between your laptop and phone. The company storing the vault can't read it.
When you visit a login page, the manager fills in the right password. When you sign up for something new, it generates a long random one and saves it.
Getting started without the pain
Most managers can import passwords saved in Chrome, Edge, Safari or Firefox. Do that first, then turn off the browser's own password saving so you don't end up with two lists.
Don't try to change every password in one evening. Start with email, banking and anything that stores a card, then fix the rest as you log in to them.