Well, first, find a good manga app from your app store. Some popular ones are Manga Rock and Webtoon. Once you have it installed, look for the search bar and type in the name of the manga you want. Make sure you have a stable internet connection for smooth reading.
There are a few. Tachiyomi and Crunchyroll Manga are worth checking out. Tachiyomi is known for its customization options, and Crunchyroll Manga offers simulpubs of ongoing series. It depends on your specific preferences though.
Well, legal manga apps usually have partnerships with publishers and follow copyright laws. However, there are a lot of shady apps out there that violate these laws and are definitely illegal.