It appears even this part has poor instruction for the beginner. I have imported images which are visible for an instant and then go black.
Moving to Light room
This issue occurs when Auto Tone has been applied to your images.
For existing photos, select all your images in Grid view, and then click the Reset All button in the Quick Develop panel. Then, click the Auto Tone button to properly apply this feature.
To prevent this issue from occurring in the future, choose Lightroom > Preferences > Presets (Mac OS) or Edit > Preferences > Presets (Windows). Reselect Apply auto tone adjustments.
Related link: Thumbnails are black in Lightroom CC 2015.2/6.2
Let us know if that helps.