Enter the email address you use for email and click Sign in.
The window will return asking for your password. Enter it and click Sign In again.
A window will pop up asking if you wish to save your credentials. Clicking Yes will allow Skype to log in automatically when you start. If you click No, you will have to enter your password every time to log in to Skype
The first time you log in with Skype for Business, a window will pop-up with a quick slideshow on how to use some of Skype's most popular features. It is very helpful and recommended to go through it.
Skype should auto-populate your contact list with your team. You can also add distribution groups to your contact list. In the search box above the contact list, type the name of the group you wish to add. Right-click the group in the results window and click "Add to Contact List".