The suffix pa, pä is often used when answering back or even arguing. For example, if someone says Tämä ei ole kallis (This is not expensive) and you wish to claim that it indeed is, a natural formulation is Onpa or Onpas. It could be used alone or as part of a longer sentence, such as Onpas se.
However, the suffix pA has many other uses, too, and they are difficult to describe. We can use Onpa se kallis as a standalone expression, without arguing, just stating “Oh, it is expensive”. This may express surprise or just emphasize the observation. This suffix is a tone particle like hAn, which is described in the next section, but their usages differ. Generally, pA argues or emphasizes, hAn states.
However, pA may be used as a rather neutral suffix, too, just to make a statement in a more natural way. A statement like Se on kallis could be used as an answer or comment to something, but if you are just saying something without relating it to something said earlier, you typically need some opening phrase. In Finnish, word-like suffixes may have the role of an opening phrase.
The pA suffix is often used to “soften” an imperative. For example, the sentence Avaa ikkuna (Open the window) would be impolite in most contexts; Avaapa ikkuna is much more acceptable.
In speech, the pA suffix is often followed by the softening suffix s, e.g. avaapas.