This repository is archived and issues are not actively read. For support with issues, please check the Stardew Valley official forums: http://community.playstarbound.com/threads/stardew-modding-api-0-40-1-1.108375/
SMAPI (Stardew Modding Application Programming Interface) is a tool to help modders make changes to Stardew. It is a standalone executable which goes alongside your Stardew.exe.
<li>Make sure all requirements are installed.</li>
<li>Extract the SMAPI zip archive alongside your Stardew.exe. For example, if using Steam this would be somewhere like ‘C:/ProgramFiles/Steam/steamapps/common/StardewValley’.</li>
NOTE!: If you are using Steam and still wish to have the Steam overlay while playing, you will need to add a launch option to the game. For example, this launch option will tell Steam to use SMAPI by default: "C:\Program Files (x86)\Steam\steamapps\common\Stardew Valley\StardewModdingAPI.exe %command%
Mod developers would work off the release branch. The master branch will contain mid-version updates which could make your mods incompatable with both the current release and the upcoming releases. You should also take a look at the <ahref="https://github.com/ClxS/SMAPI/wiki">Wiki</a> for some quick modding tutorials.