It usually involves finding an appropriate extension or plugin for Chrome. Then, you might need to navigate to a manga website and use the download function provided by the extension.
For me, MangaPark is quite good. It has a user-friendly interface and a good selection of manga. However, the legality of using free manga websites can be questionable, so be cautious.
The Chrome Web Store manga downloader typically operates by scanning manga websites and extracting downloadable content. However, it's important to note that using such downloaders might violate copyright laws and pose security risks.
Webtoons is also quite good. It has a variety of genres and often updates with new content. However, the selection might be a bit limited compared to some other sites.
I'm not sure if it's legal or recommended, but some people might use unofficial or pirated sites. However, this can get you in trouble and hurt the manga industry.