We use "this" for one object (singular) which is here (near our location). Example: This is my desk. We use "that" for one object (singular) which is there (away from our location). Example: That is your desk. We use "these" for multiple objects (plural) which are here (near our location). Example: These are my children. We use "that" for multiple objects (plural) which are there (away from our location). Example: Those are your children. Hope this helps!