Learn Italian: Dammi l'olio, che devo condire l'insalata. - Give me the oil, because I have to dress the salad.

In informal spoken Italian, che is frequently used instead of perché to provide a quick reason or justification, especially right after a command like Dammi l'olio. You could perfectly well use perché, but using che like this makes your Italian sound very natural and conversational.

Why does Dammi have a double m?

The informal imperative of dare (to give) is dai or its shortened form da'. When attaching a pronoun to a short, one-syllable imperative verb like da', the first consonant of the pronoun doubles. So da' plus mi becomes dammi. You'll see this with other short imperatives too, like fa' (fammi) and di' (dimmi).

Does condire specifically mean "to dress" a salad?

Not exclusively. While it translates to "dress" in this context, condire broadly means to season, dress, or add flavor to any dish. For example, you also use it when tossing pasta with a sauce (condire la pasta) or putting olive oil and salt on vegetables.

Can I use this causal che to mean "because" anywhere I want?