Some items in the channel may show up with a red bar on the end like this:
The red bar indicates that there are one or more errors that need correcting.
By selecting the item and going to the grid view (see Step 3), you will be able to filter for errors:
Attribute values highlighted in light red indicate the errors that need correcting:
Helpful tips:
Some errors may only become visible as a result of another attribute. These are known as conditional attributes and if left empty will show up as an error.