@Angiex__1 I recommend you tackle this problem in two different ways:
The first and most important step to solving this problem, and it's a common problem, is to find yourself a subject matter expert (SME). That is to say that you should find someone in your organization who understands all the terminology in that model and who is familiar with your system (both the GIS and the real-world) and sit down with them and have them help you pick the right names for everything. If you are friends with an engineer or someone who spends a lot of time in the field, they are often an excellent resource for these kinds of exercises. The online data dictionaries also have descriptions for most of their asset groups and asset types, but since every utility company uses their own terminology and slang for their equipment its often difficult to parse that out into some of the industry standard classifications found in that model.
Second, let the model guide you. There are rules defined for everything, so if you look at the rules and look at your data (and how you've classified things) and the vast majority of your features don't match, you may have picked the wrong asset group/type. When you're ready to test your mappings I recommend you do a quick prototype of them (using the approach outlined in this presentation from IMGIS). Just map your asset groups and asset types and see how many errors you get. If you get thousands of errors saying that there aren't any rules for the features you've mapped, then you should go back to your SME and see whether the problem is with your data, the mappings, or maybe you just have some weird configurations in your data that you need to account for with additional rules.
Finally, if you get stumped this community is a great resource to get answers. You'll find lots of examples in this forum where people have asked how others are modelling specific types of equipment (meters in particular), so if you get stuck and don't see your question already on this forum then start your own thread!
