If you scroll down here, there are 3 "Start from scratch" tutorial videos:
There's also a separate modding wiki with written tutorials if those work better for you (I vastly prefer written instructions), which I found much easier as a starting point than the main wiki's modding info (Which is essential, don't get me wrong, but it's more useful after you've copied some code). There are tutorials specifically flagged as beginner level.
The Stardew Valley Modding wiki (aka the Modding Tutorial Wiki or the Modding Wiki for short) is a companion to the Official Stardew Valley Wiki. You can think of stardewvalleywiki.com/ as a sort of "textbook" or "dictionary" containing vast amounts of useful information and as the resource for...
stardewmodding.wiki.gg
Lastly, the content patcher documentation at Github includes a guide whose very first example of a patch is how to replace a vanilla portrait. This is a bit trickier to read than the tutorials above, like the Stardew wiki is, but like the Stardew wiki, the information is extremely useful once you get into more complicated work.
Mods for Stardew Valley using SMAPI. Contribute to Pathoschild/StardewMods development by creating an account on GitHub.
github.com