Etwas vs. irgendetwas
Both etwas and irgendetwas translate to something in English, but they are not always interchangeable. The key difference lies in the degree of indefiniteness and the nuance you wish to convey.
Etwas
A1Etwas is the most common and neutral word for something. It refers to an unspecified thing, amount, or quality. It can also mean a little or somewhat when used as an adverb before an adjective.
Ich muss dir etwas Wichtiges sagen.
(I have to tell you something important.)
Möchtest du etwas Zucker in deinen Kaffee?
(Would you like a little sugar in your coffee?)
Hast du am Wochenende etwas vor?
(Do you have something planned for the weekend?)
Der Film war etwas langweilig.
(The movie was somewhat boring.)
Ich habe im Kühlschrank noch etwas Käse gefunden.
(I found some cheese in the fridge.)
Hier stimmt etwas nicht.
(Something isn't right here.)
Irgendetwas
B1Irgendetwas also means something, but it adds a strong sense of indefiniteness, randomness, or indifference. It emphasizes that it could be anything at all and the specific nature of the something is either completely unknown or unimportant. It often translates to anything at all, just something, or something or other.
Gib mir einfach irgendetwas zu lesen, mir ist langweilig.
(Just give me anything at all to read, I'm bored.)
Ich habe das Gefühl, dass irgendetwas Schlimmes passieren wird.
(I have a feeling that something or other bad is going to happen.)
Tu doch irgendetwas, anstatt nur herumzustehen!
(Just do something, instead of just standing around!)
Er murmelte irgendetwas Unverständliches.
(He mumbled something or other unintelligible.)
Wenn du irgendetwas tun könntest, was wäre das?
(If you could do anything at all, what would it be?)
Hast du irgendetwas gehört?
(Did you hear anything at all?)
Summary
In short, use etwas for the general, neutral something or a little. Use irgendetwas when you want to emphasize that it can be anything at all, which conveys a sense of randomness, vagueness, or indifference. While etwas can sometimes replace irgendetwas in a sentence, doing so will remove the specific emphasis on the any or random nature of the object or action.