TL:DR - if you've seen the movie or you are a manga reader who prefers manga, then read koe no katachi, or maybe both, first watch the movie, then read it.

So I have seen the movie for Koe No Katachi and to me it felt a bit incomplete, then I see a bunch of recommendations online to read the manga, so I did, and for a new manga reader, it was amazing.

The story is about a young 18 year old boy named Ishida Shouya who, in the first pages, we see him trying to find a girl named Nishimiya Shouko, she feels as she doesn't want to talk to our protagonist, in the next pages... well... you can see for yourself if you don't want many spoilers, but the main point of the story is about redemption, regaining something wich was lost, and that is the goal of our protagonist.

Each character gives their opinion on how they see the relationship between the main protagonists, wich gives the reader something to reflect. How much should be given to show your regret? Should you be forgiven? Even if you give it your all, does it still mather? Those are some of the questions that our protagonists have to deal.

The art is really expressive, I wasn't expecting because the only other manga I had read was the part 2 of jojo, I could feel the emotion of the characters every table

I would recommend the manga over the movie, it is far more complete and emotional.