'After' is a preposition. Prepositions are followed by nouns. 'Afterwards' is an adverb. Adverbs don't need to be followed by anything. They can stand alone. We went for a walk after lunch. We had lunch, then we went for a walk afterwards. I'm guessing from your question about 'toward' that you are more used to US English. In fact, in British English there is always an 's' at the end. There is no difference in meaning between the two variants. Both forms are used in US English. British English only uses 'towards'.