Iets is basically the same as something, namely;
However, in certain situations where in English you would can use both something and anything iets can also mean anything, e.g.:
- Do you want something/anything to drink? - Wil je iets drinken?
In this sentence if you use anything, I buy anything, you are saying that you buy something no matter what that something is. There is not really a single word that translates to that in Dutch, in Dutch you would then use in this context om het even wat or wat dan ook.