A preview of the citation for the record you have selected in the citation style you chose from the Tools dropdown menu should appear at the bottom of the Summary sidebar on the right side of the screen. If it doesn't appear, click the arrow in the bottom right corner.
Use the preview to check the citation for errors before you add it to a bibliography.
Check for these common errors and correct them in the Reference tab:
Author's name in the wrong order (First name, Last name instead of Last name, First name)
Organization name listed in the Author field (to display correctly, add a comma after the organization's name)
Email address included in the Author field
Multiple URLs in the URL field (this does not indent correctly)
Missing information (e.g., no volume number, no journal title)
Selecting Citation Styles Using Copy and Copy Formatted