Forget password

Hi!

So that's the problem: I bought a Macbook about a month or two ago, I installed a password, and yesterday I wanted to reinstall Microsoft Office on the computer, but I forgot the password. So I went online to look for tips, I did some things, and I turned off my computer. The next day, when I turned on, the first thing I had was a black screen with a box saying:

"You must enter your password to access this computer"

Suddenly, I panicked, because I forgot the password and I can not do anything on that computer without a password.

So basically, I just want an easy way to create a new account, or get this one to work.

I really need help! Thank you very much <3