The words backward, backwards, forward, forwards, outward, outwards etc can be used as adjectives and adverbs.

As adjectives

When these words are used as adjectives, they don’t have the –s ending. That means we can’t use forwards, backwards, outwards etc as adjectives. Instead we use forward, backward, outward etc.

There are many backward countries in Africa. (NOT There are many backwards countries in Africa. Here backward is used as an adjective modifying the noun countries.)
He is backward in his studies. (NOT He is backwards in his studies.)
Forward passes are not allowed in rugby. (NOT Forwards passes are not allowed in rugby.)
She was seen riding in a northward direction.

As adverbs

When these words are used as adverbs, they can be used with or without the –s ending. While the forms with –s are more common in British English, the forms without –s are usually used in American English.

Go upwards. OR Go upward.
Why are you moving backwards and forwards? OR Why are you moving backward and forward?

In expressions like look forward to, put forward and bring forward, the form without –s is always used.

We are looking forward to your next visit. (NOT We are looking forwards to your next visit.)