Ne quis sub porticu clamet, dum magistra de auctore et scriptore narrat.

Here ne introduces a negative command or negative jussive.

So Ne quis sub porticu clamet means something like:

• Let no one shout under the colonnade
• No one should shout under the colonnade

This is a very common Latin pattern:

• ne
  • subjunctive = do not / let no one / may ... not

It is not the ordinary simple negation non.
Non would just deny a statement; ne is used for prohibition or negative purpose/jussive uses.

Because after ne in this kind of sentence, Latin uses the subjunctive.

Clamet is:

• present subjunctive
• 3rd person singular
• from clamare = to shout

So:

• clamat = he/she shouts or is shouting
• clamet = let him/her shout, may he/she shout, or in this sentence with ne: let no one shout

This is not describing what someone is doing; it is expressing what should not happen.

This is a very common Latin rule.

After certain little words, Latin often uses quis/quid as an indefinite pronoun instead of aliquis/aliquid. One of those words is ne.

So here:

• ne quis = lest anyone, so that no one, or in a command-like sentence let no one

This is the same general pattern seen after words like:

• si
• nisi
• num
• ne

So although learners often expect aliquis, quis is exactly what Latin normally wants here.

Because Latin often uses the singular quis to mean anyone or any person in a general sense.

So ne quis clamet does not mean only one specific person must not shout. It means:

• let no one shout
• nobody should shout
• no one at all should shout

English does the same kind of thing with anyone and no one, which are singular in form but general in meaning.

Because sub can take either the ablative or the accusative, depending on the meaning.

• sub + ablative = under in a location sense, with no movement
• sub + accusative = to under / beneath, showing motion toward

Here the idea is location: someone is shouting under the colonnade, not moving to a place under it.

So:

• sub porticu = under the colonnade
• if it were motion, you might have sub porticum

Porticu is the ablative singular of porticus, -us, a 4th-declension noun.

That can confuse learners because:

• many 4th-declension nouns have an ablative singular in -u
• porticus is also feminine, which is worth noticing

So the parts are:

• porticus = nominative singular
• porticu = ablative singular

Used with sub, it gives sub porticu = under the colonnade / under the portico.

Here dum means while.

So:

• dum magistra ... narrat = while the teacher is telling / talking ...

Latin dum can have more than one meaning in different contexts, especially:

• while
• as long as
• sometimes until

But in this sentence, with the straightforward present indicative narrat, the natural meaning is while.

Because this dum clause is a simple time clause stating what is happening at the same time.

So Latin uses the indicative:

• dum ... narrat = while ... is telling

There is no special uncertainty, wish, or purpose here. The sentence presents the teacher’s speaking as a real event in progress, so the indicative is the normal choice.

Because they depend on de, and de takes the ablative.

So:

• de auctore = about the author
• de scriptore = about the writer

Both nouns are therefore ablative singular.

This is a very common Latin pattern:

• de + ablative = about / concerning / down from / from

Here the meaning is clearly about.

Yes, though the meanings can overlap.

• auctor often means the originator, creator, authority, or author
• scriptor more literally means writer, someone who writes

In many contexts both can refer to a person connected with a text, but auctor can suggest the person as the source or originator, while scriptor stresses the act of writing.

So using both words together may be intentional, perhaps distinguishing two roles, or simply mentioning two related ideas.

Magistra is the subject of narrat.

It is:

• nominative singular
• feminine
• from magistra = female teacher

So:

• magistra narrat = the teacher tells / is telling

If the teacher were masculine, Latin would normally use magister instead.

Latin word order is more flexible than English word order, because the endings show the grammatical relationships.

The basic structure is:

• Ne quis sub porticu clamet = main clause
• dum magistra de auctore et scriptore narrat = time clause

A very literal breakdown is:

• Ne = let ... not
• quis = anyone
• sub porticu = under the colonnade
• clamet = shout
• dum = while
• magistra = the teacher
• de auctore et scriptore = about the author and the writer
• narrat = is telling

Latin puts ne quis first to signal the prohibition right away.
It places sub porticu before clamet, which can give a natural emphasis to the place where the forbidden action would happen.