To preview your ads, ad groups, campaigns and (negative) keywords head over to the 'Text ads' tab, select a campaign from the list and click the 'preview' tab of that campaign.
This will redirect you to the tab where you can see how your ads will appear when exported to Google.
To filter on errors in preview ads, select 'By Error' from the Filter drop down menu. Now you see ads that contain errors and you can open individual ads to see where the error lies.