The best way to check how your broadcasts looks before you send is to send a test email to yourself. Click the Send test email button, here:
Choose your test email address and hit send.
If you wish to test any personalization, you can set a value under the 'Which contact should we impersonate?' option. This can be left blank if no personalization is to be tested.
Once you are happy with how the email looks when received in your inbox and browser, you can send the email. Make sure you double check your conditions before live sending.
If you want to preview your email in the browser before sending it, go to Settings and you can use the Preview in browser button found in the email settings.
This will show you how your email will look to your recipient when viewed in the browser.