In what context is ":" or, ";" used in? [closed]

From Lewis Thomas's essay on punctuation (By "the Greek usage" in the first paragraph,
Thomas is referring to the fact that Greek uses the semicolon as a question mark.)

I have grown fond of semicolons in recent years. The semicolon tells you that there is still some question about the preceding full sentence; something needs to be added; it reminds you sometimes of the Greek usage. It is almost always a greater pleasure to come across a semicolon than a period. The period tells you that that is that; if you didn't get all the meaning you wanted or expected, anyway you got all the writer intended to parcel out and now you have to move along. But with a semicolon there you get a pleasant little feeling of expectancy; there is more to come; to read on; it will get clearer.

Colons are a lot less attractive for several reasons: firstly, they give you the feeling of being rather ordered around, or at least having your nose pointed in a direction you might not be inclined to take if left to yourself, and, secondly, you suspect you're in for one of those sentences that will be labeling the points to be made: firstly, secondly and so forth, with the implication that you haven't sense enough to keep track of a sequence of notions without having them numbered. Also, many writers use this system loosely and incompletely, starting out with number one and number two as though counting off on their fingers but then going on and on without the succession of labels you've been led to expect, leaving you floundering about searching for the ninethly or seventeenthly that ought to be there but isn't.