Hello Ross,
if your Excel file is saved as CSV (which Contact files quite commonly are) you can import the contacts using the Menu>File>Import>Import contacts from. csv file option.
Choose the file, choose the folder into which to import them (best idea might be to create a new folder for these contacts in your Local folders).
When the contacts are imported, go into the folder, clock on one contact, press Ctrl+A to Select all and right-click>Create Distribution list.