Step one: burn your template
Not to be blunt, but if you really want to generate a WBS the first thing I'd do is burn the template you've been given, as it's going to lead you down the wrong path and will result in a product that doesn't do what it's supposed to. The template is conflating a WBS with a schedule; this is bad because they are complementary products meant to convey different information.
Definition of a Work Breakdown Structure (WBS)
A work breakdown structure is a hierarchical decomposition of a project into it's sub-elements. The main rule of the set of elements at any given level of decomposition is that they must completely describe the project (i.e. nothing is left out) and must be mutually exclusive (i.e. the same work is never represented in more than one bucket).
What does a CWBS contain
Given this definition we can derive what information should be in a WBS and what should not. All a WBS should contain is a title for each element that summarizes the effort, an identification number that locates with work within the hierarchy, and about a paragraph of text describing in more detail the WBS element (some people use WBS to mean just the ID and title and use the term WBS dictionary when the description paragraphs are added). Wikipedia has a good example of an ID and title only WBS for a bicycle:
So back to that template
The trap the template is asking you to fall into is to use the WBS as a schedule by asking for dates and effort. A WBS doesn't care when its elements are completed--or how much work it will take to do them; all a WBS is trying to do is to define and decompose the work into small enough chunks to support detailed planning.
So start with your project, think of how the work is logically decomposed, and keep going until you think you've gone far enough. (If you're wrong you'll find out later and can iterate, but without knowing what your project actually is or how your company manages we can't help much more than to say go with your gut.) I think if you think about creating a WBS without worrying about scheduling or hours it will go much easier for you.
If the WBS doesn't have all that schedule stuff in it then what?
The WBS is only a critical first step. Once it's complete you need several other project management products. You need to understand the organization that will be executing the work; often, this is called an organizational breakdown structure, but unless you're standing up a new group just for this project simply understanding your current organization is probably sufficient.
Next I'd create an Integrated Master Plan and Integrated Master Schedule. The plan is a more time- (i.e. event-) based way of looking at the work than the WBS. For example, our WBS example has an element for Frame Set. Frame Set might include the effort for procuring raw materials, bending metal, welding, priming, painting, drilling holes, and packaging for shipping. This all makes sense in one WBS element, but in terms of an IMP or IMS these steps are occurring over wide spans of time. The IMP and IMS take the work described in the WBS and define the logical order in which the discrete steps have to be completed. It is only once this IMS has been defined that it makes sense to start scheduling tasks and assigning resources (e.g. people, shops, etc.) to complete them.
Often the WBS is reflected graphically, but anything that can depict a hierarchy works fine, including word or excel. The reason your company's templates look the way they do is because they're calling their template a WBS, but they are really looking for a schedule--or more specifically an earned-value baseline, but that's another topic entirely.
I suggest you build your WBS first, and then use that to help you build a schedule that accounts for all the work.