Every German noun has an article: der (masculine), die (feminine) or das (neuter). The good news: the ending of a word often gives the article away. The rules below work for most words, but there are exceptions. The safest method is to learn every noun together with its article; in the app the articles are colour-coded: der blue, die red, das green.
die Wohnung (flat, apartment), die Abteilung (department (in a store)), die Packung (packet, pack), die Kreuzung (crossroads, intersection), die Kleidung (clothing, clothes), die Zeichnung (drawing)
die · nouns ending in -heit / -keit
die Essgewohnheit (eating habit), die Sehenswürdigkeit (sight, tourist attraction), die Gesundheit (health), die Krankheit (illness, disease), die Fröhlichkeit (cheerfulness), die Mehrsprachigkeit (multilingualism)
die · nouns ending in -schaft
die Mannschaft (team), die Nationalmannschaft (national team), die Landschaft (landscape), die Gesellschaft (society; company), die Wirtschaft (economy), die Freundschaft (friendship)
die · nouns ending in -ion / -tät
die Endstation (terminus, last stop), die Information (information desk), die Station (ward (hospital)), die Portion (portion), die Spezialität (speciality), die Reklamation (complaint (about a product))
die · female job titles and people (-in)
die Enkelin (granddaughter), die Freundin (friend (female); girlfriend), die Nachbarin (neighbour (female)), die Schwägerin (sister-in-law), die Kundin (customer (female)), die Verkäuferin (shop assistant, saleswoman)
das · diminutives in -chen / -lein
das Mädchen (girl), das Brötchen (bread roll), das Hähnchen (chicken (dish)), das Plätzchen (biscuit, cookie), das Würstchen (small sausage), das Schnäppchen (bargain)
das · nouns ending in -um / -ment (mostly loanwords)
das Zentrum (centre, city centre), das Kompliment (compliment), das Instrument (musical instrument), das Museum (museum), das Gymnasium (grammar school (prepares for university)), das Stipendium (scholarship)
der · days (der Montag …), months and seasons
der Dienstag (Tuesday), der Donnerstag (Thursday), der Freitag (Friday), der Mittwoch (Wednesday), der Montag (Monday), der Samstag (Saturday), der Sonntag (Sunday)
der · nouns ending in -ling / -ismus / -or
der Motor (engine), der Konditor (confectioner, pastry chef (male)), der Flüchtling (refugee), der Rassismus (racism), der Säugling (infant, baby), der Autor (author (male))
der · people made from verbs (-er)
der Verkäufer (shop assistant, salesman), der Bäcker (baker (male)), der Lehrer (teacher (male)), der Mieter (tenant (male)), der Besitzer (owner (male)), der Fahrer (driver (male))
What about words without a rule?
For words without a rule, the only way is repetition. In der/die/das mode a noun is shown without its article and you choose it; the words you get wrong come back more often.