I would start here: https://www.wikitree.com/wiki/Category:Confederate_Army%2C_United_States_Civil_War and find the appropriate state and then regiment for your profile, the one in question looks like he belongs in Mississippi, in the 34th regiment.
To add a category, click the category button on the edit page and start typing to find the correct category :
To add a sticker for your veteran you can use https://www.wikitree.com/wiki/Template:US_Civil_War
Hope that helps, I'm not great at explaining things.
Edited to add : Specifically for William it appears to me his sticker should look like this
{{US Civil War
| enlisted = 18 March 1862
| mustered = March 1865
| side = CSA
| regiment flag = Civil_War_Flags-28.jpg
| regiment name = 34th Regiment
| rank = Sgt
|unit=34th Regiment, Mississippi Infantry}}
and he should be in the category [[Category: 34th Regiment, Mississippi Infantry, United States Civil War]] and maybe the [[Category:Freemasonry]] as well, since his obit there mentions being a member of a masonic lodge.
