In Fable II this can be done by selecting the "Gift" expression on the Expression Wheel whilst interacting with and NPC.
In Fable III you must give it to them directly by interacting with them and then pressing the Gift button. If you are referring to quest items and how to give them to NPCs you must first follow the trail to find it then return it to them using the respective button (used to interact with NPCs).
However, if you are trying to gift another player a gift you must face them and press the give gift button then you will be sent to the Sanctuary. In this special room of the Sanctuary you must walk up to the item you wish to gift then select it and confirm your choice.
In future please be more specific so we are able to answer your question faster and more concisely.