If you can touch it, use "this [one]." --> This one on my desk is blue. If you cannot touch it, use "that [one]" --> That one over there across the room is red. "one" here is a pronoun that stands for something like 'pencil.'

"This" refers to a thing close to you, while "that" is used for things farther from you. This is a pen. - it's here, close to me That is my friend over there, - he isn't standing next to me, there is a distance between us Hope this helps.

I think "this one" is closer, "that one" is further. I'm not good at English, but I hope it will be helpful to you. :)