The difference is to do with mainly size and sometimes material.
Kesto: generally bigger containers; crates, chests. Includes things like mailboxes (leterkesto), and drawers (tirkesto).
Skatolo: smaller containers; cereal box, jewelry box, match box, etc. also tin cans, or other types of containers.
La vorto "ujo" can ankaŭ be used synonymously in most places skatolo and kesto are used, also kesto seems to take favour whenever there's uncertainty.
In most languages in many cases "this" and "that" can be used interchangeably. "What do you think about this/that idea?" I have been VERY frustrated with Italian questo/quello this/that, I always seem to get that wrong because I don't feel any difference (and being Dutch where the difference is even smaller).
Tiu means 'that', usually with something after it: tiu auto that car, tiu domo that house. When alone it can mean either 'that one', 'that (thing which is obvious from context)', or 'that person'. These correspond with kiu which can mean 'which (one)' or 'who'.
Manĝu terpomojn kaj feliĉiĝu!