Transferring videos from PC to iPad Pro

I have synced mp4 videos to my iPad Pro, using the Apple Devices app, according to instructions. They appear in the app, under Movies, but don't show up on the iPad. I have heard that using iTunes will remove content from the iPad. Is this true? Also, posts that give instructions regarding using iTunes are older, and the app seems to have changed. I am not overly familiar with Apple, so this is puzzling to me.