In a new install, the default membership provider is set to Multiplexing (a mix of Windows and SQL membership), so you should be able to login with your Windows credentials (assuming your user is a local Administrator on your computer. After logging in, you can access Admin mode and create new (SQL) users.
Info about the built-in roles required to gain access:
In-depth about the provider system:
Thank you so much for your help Arild!
Your answer is very helpfully.
I´m triying to create a new site based on WebForms template and I can not being able to enter in edit/admin mode.
When I created a new one with the MVC template, the first time I could create an admin user but in webforms I can not beeing able to do that.
Any help or guidance will be usefull because it´s my first time with episerver.