Settings - Image Conversion - Image Quality. What does it mean?

[GoldenNeko]

Hi! I downloaded a few manga and noticed a small detail that bothered me; in the [Settings] tab you can choose [Save to] and then [Conversion Rules] and then [Convert to] that lets you choose the format and [Quality] which was set to 80%. Does this mean I downloaded manga in 80% quality? If I change it to 100% and download it again it will be in a better quality? What king of format should I choose (png. , jpg , jpeg , webp.) to get the best possible quality?

Thank you for your help!