That kind of error messages can be frustrating, as it takes more than a little knowledge on the subject to understand exactly what is wrong. Usually, however, the problem is either the authentication (invalid username/email/password) or that there’s a problem with git (locally).
First of all, check that you have git installed by running “git” from the command prompt. This is a more common mistake than one would think.
Second, try y.bedrov’s suggestion. Log in to github.com on the web. Settings -> Developer settings -> Personal access tokens. Create a new token and then, in IntelliJ, select Enter Token at the login prompt.
Tokens are considered a more secure way to authenticate, I believe.