Q: I cannot select more than one message at a time to delete from the trash. Any ideas will be appreciated

Hold down the shift key while clicking on the list (bottom to top to select all).

This works in many different ways and in lots of apps.

Hold down the command key and you can select from a list (leaving some not checked) to exclude them from the delete process.

To empty all of the trash folder use command-a keys to "select all" and then the delete key to remove them.