Words like backward(s), forward(s), northward(s), outward(s) etc. can be used as adjectives or adverbs.
When they are used as adjectives, they do not have –s.
- African countries are backward in some ways.
- He was last seen driving in a northward direction.
When these words are adverbs, they can be used with or without –s.
- Why are you moving backward(s) and forward(s) ?
- If we keep going upward(s) , we will get to the top.
In figurative expressions such as look forward to, bring forward, put forward, the form without –s is always used.
- She put forward a very interesting suggestion.
- I look forward to hearing from you.