Hey @ckrkmz, welcome to the Ghost forum!
Generally, a bit more context would always be appreciated 
In your case, the problem is in the missing Mailgun setup (see “Mailgun is not setup”)
In order to send newsletters, you need to set up Mailgun, since that is used for sending these emails: Why do I have to set up Mailgun for newsletters?
Simply sign up on the Mailgun website (the pay-as-you-go plan is a bit hidden), retrieve your Mailgun API keys, click on the “Edit” button in your Ghost Mailgun settings you see on your screenshot, and you’re good to go.