Is afterwards formal?
The first would be more common in formal written English. Both are common in spoken English. However, the two words afterwards and after are not interchangeable. The preposition afterwards is intransitive and doesn’t take a complement.
Do you say toward or towards?
The only difference between toward and towards is the s. Both spellings are correct, and they mean the same thing: in the direction of. Toward is the preferred spelling in the United States and Canada. In other English-speaking countries, such as the United Kingdom and Australia, towards is the more common spelling.