Hello!
To use mods (given you have smapi),
1. Download the mod (manually) you want on
https://www.nexusmods.com/stardewvalley. You must have an account (sign up is free) to download mods.
2. Make sure you download the Nexus requirements (and the dependencies of the requirements too).
3. It is advisable to observe the last time the mod-creator uploaded his/her mod. You may also want to check the "posts" and "bugs" tab to know if the mod is still up to date and etc..
4. Extract the mod/s. Drag the extracted mods or folders
in your StardewValley/Mods.
5. Run smapi. Play the game! :)
Here's a simple tutorial:
[Windows]
-
https://www.youtube.com/watch?v=GICMNzJRSbk
-
https://www.youtube.com/watch?v=WdUpFwbSJks
[MacOS]
-
https://www.youtube.com/watch?v=S1pYyuynnpg&t=37s
-
https://www.youtube.com/watch?v=Ant428S6p4Q&t=118s