@boreal oar Sure thing.
So the first thing you do is creating the page. This is easily done by clicking the red link that indicates a missing page. Doing this will automatically link the page with the items.
Next is filling the page. At the moment all units are categorized by type of the unit, into one page. So as you have seen, all the siege units should be described on one Siege page (currently only 2 siege units).
The template I use per unit is called TroopPage. You can add this with the Visual Editor by using the "insert" to insert a template. Though I suggest to use the Source Editor as this rightfully shows all the needed parameters. The Source Editor can, again, be accessed by the blue arrow next to "Edit".
I have manually placed a header above this template. So for example, you get this Wikitext in total for the "Battering Ram":
== Battering Ram ==
{{TroopPage
|Battering Ram|type=siege
|age=Stone Age
|attack=60
|defense=120
|health=120
|marchspeed=Very Fast
|load=20
|power=1
|skill1=City Destruction
|skill1description=Siege Unit, restrains watchtowers, but is restrained by infantry, archer and cavalry units.
|skill2=Weight-bearing
|skill2description=The structure of siege weapons allows them to carry more resources
|description=Simple structure that can inflict huge damage on wooden gates. A nightmare for many cities.
}}
skills can go up to 4,. I think the parameters are self explanatory. Let me know if they are not.
Currently on the Siege page (https://riseofcivilizations.wikia.com/wiki/Troops/Siege) I have used this 2 times as you can see.
Let me know if this explanation is enough. You can also go to the siege page and look in the Source Editor as a reference point.
Feel free to ask more ^^