Usually when you are asked to create a password, they want you to make a secure password. Secure passwords are hard to break by brute force (simply guessing) or by dictionary attacks where they guess words in the dictionary. In addition, it is strongly suggested you use different passwords for different sites so if your email provider has a breach and your username and password stolen, then they will not automatically have access to your bank account for instance.
The rules are usually that the password must contain upper case letters, lowercase letters, numbers and special characters. Sometimes all four are required or three of the four. Also, the length normally must be eight or 12 characters. This stops people from using the most common passwords like password and 12345678 which actually are used a majority of the time shown by studies.
If you are like many people, your comment now is how do I come up with one that I can remember? I might make a 1Wr1t3@L0t for my password if I had to use one to submit my article to the newspaper. Now to show you how I came up with it and how easy it would be for me to remember. Notice it is 10 characters long, so if rule is the password has to be at least eight it is ok. I have included upper case letters, lower case letters, numbers and special characters.
First, I came up with a phrase related to the site that is at least eight characters long. I chose I write a lot. I then made that one word. Iwritealot. Notice for someone just seeing it is already getting garbled, but we know what it is.
Next, I change letter a to @ and that will be easy to remember but someone looking at probably not see how fits. Iwrite@lot. Then I change I to 1 and o to 0 (letter to number) and have it further mixed but still clear to us. 1wr1t3@l0t is now the password. Now I have letters and numbers and special characters.
Next, I will change the first letters of words to sentences. It now looks like 1Wr1t3@L0t. Now I have met all the rules and made a secure password I can remember.
Another way to start this is come up with an eight-word phrase and then use the first letters. I enjoyed attending Winthrop College and graduating as an eagle. That phrase is true about my college life and so I could remember it. Taking the first letters I get IeaWCagaae. That already looks hard to guess or break but easy for me to remember. I then do all the items from above and end up with I3@WC@@3 which looks totally confusing to anyone but me since I know the phrase and conversion.
This should make it easier for you to develop secure passwords you can remember.