Can somebody give an example of work items and activity codes that are used in Work Breakdown Structure? Thank you.

IIRC items are for billing/breaking down the project (e.g. data prep, data load, implementation, post-implementation support (stuff that you want your customer to see)) and activities are how you break down your expenses and time for things you want to be able to see across multiple projects (e.g. traveling, client meetings, data work). They both really could be just about anything, really depends on what the business is and what needs to be tracked and reported on.

Thank you. It sounds like work items can be the same with project tasks?

There's no point to using both if you're going to use them for the exact same thing IMHO. I think the functional difference is where they show up on entry, how they translate to billing, and what transactions they're available for expense/time entry.