Great. I'll have to look at mods are they via steam or that nexus thing.
Various sources. There are currently 422 on Nexus, which is where I get all the mods I use in all the games I use mods on.
https://www.nexusmods.com/valheim/mods/
Modding Valheim is currently more complicated than modding many of the games for which modding is more established. You will often have to download resources from more than one site (e.g. many Valheim mods require BeplnExPack from https://valheim.thunderstore.io/package/denikson/BepInExPack_Valheim/ to be installed) and you'll probably have to install Valheim mods manually. Some will install simply through Vortex, Nexus' mod manager, but some won't. It's still early days for Valheim modding.
I haven't used any Valheim mods yet, but I have about a dozen bookmarked for consideration. A mod that allows you to cycle through snapping points on a building item you're holding or looking at so you don't have to get into an angle from which you can point the cursor at the desired snapping point. That would be very handy for building. A mod that causes food bonuses to remain constant for half the expiry time and and decrease twice as quickly for the remaining half of the expiry time. The addition of a mapmaking skill that gradually slightly increases the update range on the minimap (which at default is much less than your viewing distance). Etc. I don't want to fundamentally change the game, but there are some things I'd like to change a bit.