"Afterwards" has the same meaning as "after" but its usage is much more limited. Only "after" can be used in these sentences: "I will speak to you to after lunch." [preposition] "After I speak to you, I will speak to him" [conjunction] "After speaking to you, I will speak to him" [preposition] You can use either here but "after" is sometimes considered too informal. "After/Afterwards, I will speak to you" [conjunction] or end of sentence "I will speak to you after/afterwards" [conjunction] In this case "After/Afterwards, refers to the thing you mentioned in the previous sentence.