Executable files are files that can be used to run a program or to do a specific purpose specified in the file. Normally not all files defaultly would be executable in Linux because of security reasons. If all files are defaultly executable then the scripts can do whatever the hell they want to do in your computer. As we call them VIRUSES. This is one of the main reasons why you should use Linux. It’s virus free.
If you want a file executable you can do it with a simple trick in Ubuntu.
Right click on the file and click Properties. Choose the tab Permissions and click on Allow executing file as program.
After clicking close the dialog. Now the file is executable. While opening the file you will get a dialog :
You want to execute the file so click Run in Terminal.