People forget passwords - it happens to the best of us! Luckily, we have a few ways of helping people log in, even if they don't know their password.
As an end user, everyone is given the option of resetting their password themselves. Below the login fields is a link that says "Forgot your password?" As long as the user has a valid email address associated with their account, they can get a password reset link emailed to them by clicking on that link.
As an admin, you can also manually send a password reset or new invite to anybody with a valid email address.
First, navigate to the Admin section using the Application Switcher in the upper right. From there, click on Users & Permissions and in the menu that appears, click Manage Users.
Click on the user whose password you need to reset. In the upper right is an envelope icon; click on that to get a box where you can send a Custom Email. Click on the Custom Email dropdown to get a menu that looks something like this:
Click on the second option and then click Send to email the user. They will get a link to set their password, just as if they requested it themselves.
Note: This may look slightly different if the user has never logged in: the second option will say "Invite" instead of "Password Reset Request"
Both of those options require that the user has a valid email address. If they do not have an email address, then you will need to set the password yourself. This requires doing a user upload with a password column. See the linked article for more information on how to do this.