Both 丢 and 扔 have the same meaning when used to indicate to litter.They're interchangeably
But, 丢 has another meaning, which is lost. Chinese learners sometimes get confused with these two words.
- 我丢了我的旧皮夹 (I lost my wallet)
- 我扔了我的旧皮夹 (I threw my wallet away)
Hope they help,