The comma (,) is used to divide sentences or clauses which form part of one main thought.
Monica told him that, if he wished to gain friends, he must so act, that people could know that he was well-disposed towards them.
Also to separate nouns used consecutively in a list, as:
The salesman sold paper, pencils, sharpener, pen and ruler.
Note that there is no comma after the last noun but one, before and.
The semi-colon (;) is used to divide sentences complete in themselves, when the idea conveyed by the whole is continuous.
Dukhu used to live alone; he contrived to satisfy his immediate wants by hunting and fishing; he never saw any human being for a very long time, and consequently suffered much from loneliness.
The colon (:) is used generally when the sentence following is a summary or explanation of the preceding one, or before a list of things.
Monica went to market and bought the following articles:a dozen eggs, a bottle of soda-water and a pound of cheese.
Also usually before quotation commas, as:
Monica said: “The car has gone.”
FULL STOP [.]
The full stop (.) is used when we wish to show that the idea concerned in the sentence is complete. If the next sentence begins an entirely new thought, begin it on a new line; if the stop is at the end of a line, begin the new sentence a short space from the beginning of the next line.