Die Welt is a magazine in Germany. It translates to "The world".
die is a feminine definite article (like 'the' in English). In German language you have three genders: masculine, feminine and neuter, and the definite articles in nominative for these three genders are der, die and das.
When you use words that specify quantity, the plural of the word is not used. The word stays in singular.
Katze means 'cat'. Plural 'cats' in German is Katzen. There are many rules on how to create plural from singular, so I suggest you learn the plural version of a noun as you learn the noun (along with the gender).
einen here is the indefinite article in accusative. We will talk about accusative, one of four cases in German, very soon.
Key phrases
Wie viel kostet die Zeitung?
Hier ist das Geld.
Hast du Haustiere?
Ich habe einen Hund.
Wie alt bist du?
Ich bin zehn Jahre alt.
Questions
1. Wie _ _ _ ? bist du? 2. Was _ _ _ _ _ _ ? die Zeitung? 3. Ich habe _ _ _ _ _ ? Hund. 4. Ich bin zehn _ _ _ _ _ ? alt. 5. Ich _ _ _ _ _ _ ? zwei Bier bestellen.