The German adjectival prefix Extra- can often be translated as the English adjective "extra." If you wish to use "extra" as an adjective in German, it is not usually a freestanding word (excepting certain anglicisms such as extra dry) but is instead added to whatever noun is being modified. Let's first take a look at examples of the German adjectival prefix Extra-:
Niemand hat einen Extrapullover für Catherine?
Nobody has an extra pullover for Catherine?
Caption 49, Deutschkurs in Tübingen: Die Konjunktion "dass"
Ein Extrapaar Schuhe ist auch immer praktisch.
An extra pair of shoes is also always practical.
Caption 21, Christiane: fährt in den Urlaub
Note that it would not be correct to write extra Pullover or extra Paar, instead the adjectival prefix Extra- is placed together with the noun: Extrapullover and Extrapaar. In some cases where extra is required to modify another adjective, it is still written in lower case, such as in extragroß ("extra large") and extrastark ("extra strong").
The German adverb extra, however, is usually a false friend, meaning it is written the same way in both languages but has a different meaning:
Die habe ich dir jetzt extra geholt, jetzt komm schon.
I got it especially for you, now come on.
Caption 58, Die Pfefferkörner: Eigentor
Ach so, stimmt! Extra hergeflogen aus Saudi-Arabien.
Oh, that's right! Especially flown here from Saudi Arabia.
Caption 30, Fasching: mit Cettina
As you see in the above examples, the German adverb extra is usually translated into English as "especially." However, sometimes the word "especially" is a bit too simplistic for the context, and it is better to use a more tailored translation such as "for the occasion" or "for that reason":
Manfred Schoof hat extra eine einfache Melodie komponiert.
Manfred Schoof composed a simple melody for the occasion.
Caption 5, Bibliothek der Sachgeschichten: Müllmännerlied
Die Hölzer kommen dort meist nicht von extra angelegten Plantagen.
The wood there does not usually come from plantations cultivated for that reason.
Caption 27, Umweltschutz: WWF zur Rettung des Regenwaldes
Come up with a good phrase that you can use as a mnemonic device for remembering the difference between the adjectival prefix Extra- and the adverb extra. Here's such an example that works for me — as do most things chocolate:
Ich habe einen Extrariegel Schokolade extra für dich mitgenommen.
I've taken an extra bar of chocolate along especially for you.
Look for other examples of the German adjectival prefix Extra- and adverb extra in use in a real-world context on Yabla German and learn some other ways in which the word can be used.