Is there a way to make a file read-only from dired?

This, this, and this are unclear to me.

The manual has lots to say about marking/flagging via dired as well as operating on files, but I can't see anything in operating that discusses changing a file to read-only.

Based on the links above (that I said were unclear to me), I am guessing it has something to do with modes and/or permissions?

For bonus points, is there a way to operate on a directory via dired to make all files within it read-only?

To be clear, I want the files to become read-only and to stay that way until they are changed back to read/write manually.