To open a file, choose File → Open. A new tab containing the file will appear in the work area. You can use this to edit the file.

To run a program from a file, choose File → Load and Run.... This will run the program without opening it in a separate tab. This is equivalent to the load command.

If you have made edits to a file you wish to throw away and want to reload to the version that's on disk, you can choose the File → Reload from Disk menuitem. This is useful for experimenting with a program and making temporary edits, to run a program, but that you do not intend to keep.