German uses compounds more often than English and they are formed by simply putting the two words together (sometimes adding an -n or -s in between), and using the gender of the last word. Die Woche (week) + der Tag (day) = der Wochentag (Days of the week)
When referring to people, adjectives can sometimes be used as nouns. The definite article precedes the adjective, which is now capitalized because it is functioning as a noun. The adjectival nouns take the regular adjective endings for adjectives preceded by a der word as well.
der Alte - the old man
die Alte - the old woman
das Alte - everything that is old
die Alten - the old people
To form the ordinal numbers, just add -te to the cardinal numbers for 1-19, and -ste for 20 and up. The exceptions are erste, dritte, siebte, and achte.
In writing dates, German uses the number followed by a period. On February 2nd would be am 2. Februar. However, when saying this out loud, you would say am zweiten Februar. You must use the construction am + -en to answer a question beginning with Wann? But you use the construction der + -e to answer the question Welches Datum?
Wann sind Sie geboren? When were you born?
Am achzehnten Mai. On May 18th.
Welches Datum is heute? What is today's date?
Heute ist der neunte Oktober. Today is October ninth.
To change a sentence from the active to the passive, change three things:
1. accusative object of active sentence to nominative subject of passive sentence
2. active verb to a tense of werden plus the past participle of verb in active sentence
3. subject to von + dative object in the passive sentence, if agent is mentioned
Viele Studenten lesen diesen Roman. = Dieser Roman wird von vielen Studenten gelesen.
Many students read this novel. = This novel is read by many students.
Viele Studenten lasen diesen Roman. = Dieser Roman wurde von vielen Studenten gelesen.
Many students read this novel. = This novel was read by many students.
Viele Studenten werden diesen Roman lesen. = Dieser Roman wird von vielen Studenten gelesen werden.
Many students will read this novel. = This novel will be read by many students.
Present Perfect Tense
Viele Studenten haben diesen Roman gelesen. = Dieser Roman ist von vielen Studenten gelesen worden.
Many students have read this novel. = This novel has been read by many students.
Past Perfect Tense
Viele Studenten hatten diesen Roman gelesen. = Dieser Roman war von vielen Studenten gelesen worden.
Many students had read this novel. = This novel had been read by many students.
*Notice that in the passive voice, the past participle of werden is worden and not geworden.
Durch can replace von when the agent is an impersonal force (fire, wind, etc.); but it cannot be used if preceded by a limiting word (such as an article or adjective.)
Passive with modals
Shifts in tense will only affect the modal part of the sentence. The infinitive forms of the past participles are used with modals in the passive voice as well. And where you might expect something like Das Haus hat werden müssen verkauft, the actual construction is Das Haus hat verkauft werden müssen because of the double infinitive construction. Double infinitives always go to the end of the sentence, but you only need to worry about these in the present perfect and past perfect tenses.