You are not stupid! I still need to add a tutorial on how interactions between characters work.
Regarding feeding NPCs, there are two things to consider. When you give them food, they will not eat it right away. However, giving them food they like will increase their friendship, and they will have gained a bit of weight on the following day.
However, when you become friend with said NPC, you may unlock the option to invite them over. When you invite a character, the rules are a bit different ; the food you give them will not increase their friendship level, but they will eat it. So you can stuff them and make them gain weight faster. NPCs you invite may also react to your character being fed.
For now, the only NPC you can really interact with is Emma. But in the next update I'll start introducing a few more characters (including Loraine) and giving Jenny a few more dialogues, events and ways to interact with her.