I strongly recommend something like 1Password (my preferences), or Last Pass also very popular and well respected.
All passwords in these apps are encrypted locally. Anything transferred via the internet is fully encrypted locally and the encrypted file cannot be seen by anyone that does not have your 1Password or Last Pass local password. The vendors cannot see what is inside your password file.
I recommend these utilities because:
A) we all have a gazillion online accounts and passwords. These utilities allow you to keep track of all of them and they make it easier to give them unique passwords.
B) many online account have security questions, URL, phone numbers, a credit card you associate with them. You can store this additional information along with the username and password so that you can find all of it in one place.
For example, if you have to (or want to) change a credit card, you just use your password manager app to find all the accounts using that credit card and you can login to each and change your credit card.
Those security questions. You do NOT and should NOT give real answers to those questions. But fake answers can be difficult to remember, so you store them in your password manager. So no one can get into your account, like was done for some famous people and political figures by guessing the valid answers to security questions. Your would be totally fake and off the wall answers that one could guess, except you have them stored in your encrypted password manager.
C) Password managers can easily keep all their passwords sync'ed across all your devices, so you always have your passwords, answers to security questions, etc...
D) you can store other secure information in a password manager, such as credit cards, software licenses codes, FileVault encryption keys, medical notes want to discuss with your doctor, copies of your drives license, and other documents or pictures of them. Anything you want to have access to, but you do not want anyone else to be able to see it.
Just make sure you give your password manager an easy to remember password phrase (multiple easy to type words) that make up a long length (the longer the pass phrase, the more secure your data is in the password manager encrypted file; don't go crazy but something in the high teens to 20's in length but easy to type and remember would be good; much better than finger twisting special characters, numbers, capitals, lowercase mix that no one can remember; length is king )
