Most will include instructions on how to install their particular mods so if you run into any problems, consult their instructions to see if anything was missed. Some mods may require additional steps if they include texture packs or other files that change the core gameplay. whenever I visit a new settlement there is a trader.
If you have not modded your game in the past, it will be set to native by default. Im currently playing through Mount And Blade 2: Bannerlord, which has an interesting smithing system.
Installing mods for Warbands is pretty easy for anyone who has modded a game before.