We can combine two very common verbs into one expression that means "to get busy" or "to work hard." The expression is darsi da fare. We can detect a reflexive ending on the verb dare (to give) with darsi. If we think about it in the first person, it's, "I give myself." What do I give myself? Da fare (stuff to do). 

If I am busy and can't talk to you right now, I might say, Ho da fare (I have stuff to do, I am busy).

Ho detto: "Senta, scusi, eh... io c'ho [ho] da fare, è tardissimo, -Mh.

I said, "Listen, I'm sorry, uh... I'm busy, it's really late," -hmm.

Caption 48, Francesca e Marika Gestualità

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But if you are giving yourself stuff to do, with the verb dare (to give) it's more active. 

Mi do da fare (I keep myself busy, I work hard).

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If we are talking about someone else who works hard in general, we might say: 

Si dà da fare (he/she works hard).

Note the accent we place on the third person singular of the verb dare to distinguish it from da, the preposition meaning "of," "to," or "from."

We also use this expression in a command form when we want someone to get to work, to do something, or to get something done. 

Datti da fare! (Get to work!, Do something! Get on it!)

Datti da fare pure tu.

You get on it, too.

Caption 13, Provaci ancora prof! S2E4 L'amica americana - Part 16

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If we are talking to more than one person, it's: 

Datevi da fare.

We might be talking to a group we are included in, we'll say:

Diamoci da fare (let's get to work, let's get busy).

If we are being polite or formal to one person, it's:

Si dia da fare.

If we want to be polite to more than one person, we need to go into the third person plural:

Si diano da fare.

Tip: Note that when we are using the polite form, it's the same as the subjunctive third person (check out the conjugation chart). We can mostly get by fine without using this polite form, unless we are working in a place where our Italian-speaking employees are people we address formally. 

To conclude, da fare can be part of a longer phrase such as Ho tantissime cose da fare (I have lots of things to do), but da fare can be used by itself to just mean "stuff to do."

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