is it possible to open jpg files in Photos on a macbook?

Photos stores photos in a "Library". If you want to use Photos, you'll need to let it create a library. It should be an option when you open it for the first time. You should then be able to to to File>Import ... and import your file.

See also:

Overview of importing photos and videos into Photos on Mac - Apple Support

Photos is a Photo library manager. You can import the photo into the Photos menu, and the imported library will show you the photos you recently imported. There you can duplicate the photo selected, and then edit it.

Sometimes when you import a photo, it actually duplicates the file into a library folder that is hidden from you called the Pictures folder, if your advanced proferences for Photos has it manage your photo library.

When it does so, any edits will impact just the photos already imported into the library.

Alternatively you can use the Preview application with its editing tools to adjust brightness of individual JPEGs and save them.

There's a whole guide for Preview.

Preview User Guide for Mac - Apple Support

P1tterP4tter wrote:

If you just want to quickly preview a bunch of .jpg's, copy them into a directory (sorry, folder), set the View to icons (the little grid symbol), and just <> arrow away.

Thomas

You're answering a thread that has been dormant for over a year. And, the OP wanted to be able to edit the files.

Good work! :)

johncla,

If you just want to quickly preview a bunch of .jpg's, copy them into a directory (sorry, folder), set the View to icons (the little grid symbol), and just <> arrow away.

Thomas