I can’t find the instructions for a link but here’s how you do it:
Open Facebook on your iphone and tap your “Menu.”
On the next page scroll down and tap “Settings and Privacy,” then “Settings”
On the next page scroll down and tap “Shortcuts”
On the next page tap “Shortcuts bar”
On the next page look at your “Available Shortcuts” and tap the ones you want to hide. On the next page tap “Hide”
Good question. The workings of Facebook news feeds is a mystery to me. I know if I look at stuff on Home Depot or Best Buy, then I start seeing these ads for these things in my news feed.