Once you have downloaded and opened the Plays.tv client, you will see 'Register' and 'Log in' buttons near the top left of the application:
If you don't have a Plays.tv account yet, you will need to Register; otherwise you can log in with your Plays.tv Account.
Registering a Plays.tv Account:
To create a Plays.tv account, you just need to provide your Email, and then create a Username and Password for your Account.
(Note: You cannot change your account name after it has been created)
Additionally, you can create an account through various Social platforms:
Keep in mind, if you use this method to create and sign into your account, and that social platform somehow becomes unbound from your Plays.tv account, you may be unable to login and should get in contact with a Customer Service Rep.
Logging into Plays.tv:
All you have to do is provide your Plays.tv Username and Password and you will be logged in. If you have one of the Social platforms mentioned above bound to your account, you can also log in by clicking on the associated button.