@apricoto: How to show that books have been read is a fairly common question here. So common, that it gets asked most weeks. A search here will find the discussions.
But, there are several common ways to do it:
- A custom Y/N column. Which is what @ownedbycats has suggested
- A custom column for the date read.
- Set the rating.
- Add a "read" tag to the tags.
- Use a custom column for the percent read.
- Use a custom column for status (such as "to read", "reading", "read" etc).
- Use the Reading List plugin and with lists for each status you track.
- Re-purpose an existing column, such as what @BetterRead does with the Date column.
Or some combination of the above. What people do depend on what they want to track. I think the first three or four are the most common methods. The rating and using a tag are probably the easiest as they do not require changes o
Personally, I use the custom date column plus the percent read column. The columns are automatically updated from my Kobo ereader when I connect it (courtesy of my Kobo Utilities plugin). Then I move the book to the appropriate Reading list (from "toRead" to "Reading" to "Finished") and set the rating when it is finished.