"I can't help but look at posts on instagram."
"I can't help but ~" 「つい〜てしまう」
"look at ~" 「〜を見る」
"posts" 「投稿」
"on instagram" 「Instagramで」
"I can't stop looking at instagram."
"I can't stop ~" 「〜をやめられない」・「つい〜てしまう」
"looking at instagram"、"posts on" つけなくてもいけます。