Learn Portuguese (Portugal): A nova lei trará a paz e a ordem.

Trará is the 'it' form of the verb trazer (to bring) in the future tense. Trazer is irregular in the future tense: instead of adding the endings to the full infinitive, we use the shortened stem trar- and add the ending -á.

Why are there as before paz and ordem? In English we just say 'peace and order'.

In Portuguese, definite articles like a (the) are almost always used with abstract nouns when talking about them in a general sense. Because of this, 'peace' becomes a paz and 'order' becomes a ordem.

Could I say a lei nova instead of a nova lei?

Yes, you can. Nova is a common adjective that often goes before the noun. Placing it before the noun, as in a nova lei, is very typical for laws or rules, though a lei nova is also grammatically correct.

How can I tell that lei, paz, and ordem are feminine words?

They do not end in the typical feminine -a, so their gender just needs to be memorized. Paying attention to the feminine article a used before each of them in this sentence is the best way to remember that they are all feminine nouns!