How do you do this? Is there specific npcs that you can donate to? I'm trying to max out some of my affinity levels and apparently this is one way to do it. Aside from that one guy in Diamond City I haven't found another one to donate to. Some people are telling me that giving (trading) to settlers is what they meant by this. But, I have been doing that and it doesn't seem to do anything.

if by donate you mean give an item to an NPC like Preston or a companion or one of your settlers in one of your settlements just ask to trade then add the item from your inventory to theirs once you are done swapping items and before you close out the trade window highlight their new items & tell them to equip the items Xbox one its the Y button then close out window

I've been doing that it doesn't seem to be doing anything. No little bubbles that pop up and tell me if a companion liked or hated that action. According to the some guides, like the Prima one, states that you can raise the affinity levels of Curie, Nick, Piper, Cait, Preston, Cogworth, and Hancock by "Donate Item". They just don't say what the hell meant by this.

The only thing I noticed is that Cait likes when you lockpick stuff or when you're beeing selfish and don't help others. Piper also like when you lockpick stuff but she prefers when you do help people instead. Presten likes when you do weapon mods and do settlement stuff. I've never noticed anything when I trade items with them.

In Dragon Age you could give items to your followers that would make them happy though. But that is Dragon Age.