For legal and free manga reading, check out sites like ComicWalker. Keep in mind that the selection might not be as extensive as paid platforms, and ads might be present.
A few libraries also provide access to digital manga for free. You might need to have a library membership. Also, some manga creators offer free chapters on their personal websites or social media to promote their work. But again, it might not be a comprehensive collection.
You might try platforms like MangaDex. But keep in mind that availability can vary and the selection might not be as extensive as paid services. Also, make sure to follow the site's terms of use.
You can try some official manga platforms like Webtoon or Crunchyroll. They offer a variety of manga for reading online legally, but some might have limited free content.