"Tiu" is for known objects.
Examples Tiu lando estas bela -> That country is beautiful. (Note that "That" is adjective of something previously known, the country)
Tiu estas bela -> "That one is beautiful". (Note that I have to use "That one" in order to still meaning something known, otherwise "that is beautiful" would mean an object not previously known by context, because I would be introducing it now)
Tio estas bela -> "That is beautiful"
Note also that I cannot use "tio" as an adjective, because in that case the object I want to modify would be known.
Regarding to the use of "ĉi": "ĉi tiu" -> "This", and "ĉi tio" -> "This". What's the difference? those explained above. (This one vs This) and (This(adj) vs This(noun))