extra
In addition to what is usual or already present; separate.
Für diesen Service wird eine extra Gebühr berechnet.
An extra fee is charged for this service.

Loading your saved state.
In addition to what is usual or already present; separate.
Für diesen Service wird eine extra Gebühr berechnet.
An extra fee is charged for this service.

'Extra' is a special adjective that is almost never declined. It keeps its basic form, even when it comes directly before a noun.
Möchten Sie eine extra Portion Pommes?
Would you like an extra portion of fries?
When 'extra' describes a noun, it usually means 'additional'. When it more closely defines an action or a verb, it means 'intentionally' or 'especially for this purpose'.
Ich hätte gern einen Kaffee mit einem extra Schuss Milch.
I'd like a coffee with an extra splash of milk.
In the meaning 'absichtlich' (intentionally), 'extra' often stands directly before the part of the sentence that is to be emphasized. This can be a time expression, a place, or another adverb.
Ich habe das Geschenk extra für dich gekauft.
I bought the gift especially for you.
The word 'extra' is very common in spoken language and informal writing. It sounds natural and is often used in everyday life.
Kannst du mir extra noch ein Brötchen mitbringen?
Can you bring me an extra roll too?
especially / special
'besonders' and 'extra' can both mean that something is not simply part of what is normal. 'besonders' often describes something exceptional or something that is treated separately. 'extra' usually means that something is additional, separate, or done intentionally for a purpose. They can be confused because both sometimes mean 'separate'. For a special value or a noticeable quality, you are more likely to use 'besonders'. For something additional or done intentionally, 'extra' fits better.

Vor dem Gespräch bringt die Klasse extra Stühle für die Gäste.
Before the meeting, the class brings extra chairs for the guests.
In der Bibliothek suche ich heute ein besonders ruhiges Zimmer.
At the library today, I am looking for a particularly quiet room.