On your first time, only have the workbook in question open. Close all other open workbooks.
From Excel, go into the Visual Basic Editor (VBE) by one of the following ways:
1. Tools>Macro>Visual Basic Editor
2. Alt+F11 key combination
Once there, hit Ctrl+R to ensure that the Project Explorer is visible. Wherever it is docked (usually on the left side), you will see a reference to your workbook. If you expand the options, you should only see a folder called Microsoft Excel Objects. Expanding further, you should see the names of the various sheets in your workbook. Each of those sheets can hold macros, but that is for later.
From the top menu, Insert > Module. In the Project Explorer, Excel will have added an additional folder called Modules. On the main part of the screen, you should see a blank sheet (or else Option Explicit), which is the code sheet (it will be called Module1 in the Project Explorer).
Copy the code for the routine into that blank section of Module1.
Close the VBE (Alt+Q) to go back to Excel.
Select the range of items in column B
Tools>Macro>Macros (shortcut key combo is Alt+F8) will bring up a dialog box. The only macro you have should be highlighted. Choose Run and the macro will process.
A lot of steps at first, but these will become second nature in no time.