Either or is fine. I do larger things like towns and stuff that require terraforming personally, so I tend to upload a worldfile.
Your world files will be in Users/(youruser)/AppData/LocalLow/IronGate/Valheim/WorldsLocal.
If you want to save a build using PlanBuild OR Infinity Hammer and upload it, those would be located in SteamLibrary/SteamApps/Common/Valheim/BepInEx/configs*
*If its IH it will be in that folder, if its PlanBuild, its in another folder at the top called 'PlanBuild'.
Hopefully that answers most of your concerns!
