When you're playing a game, you have to follow the rules. When you don't, someone might say:

Non vale (it doesn't count).

This comes from the verb valere (to have value, to be worth, to be valid).

Devi chiudere gli occhi però,

You have to close your eyes, though,

se no non vale. Vai.

otherwise it doesn't count. Go.

Captions 10-11, Sposami - EP 2 - Part 20

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So in this case, the verb valere is used to mean something isn't valid, it doesn't count.

BANNER PLACEHOLDER

But we also use it when we talk about something being worth it. In English, we can say something is worth the trouble or simply "worth it." In Italian, we need to say the whole phrase:

Vale la pena (it's worth the trouble, it's worth it).

Insomma, la vita è una cosa meravigliosa

So, life is a marvelous thing

e vale la pena viverla.

and it is well worth living.

Captions 41-42, Amiche - Filosofie

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In the previous example, we have a subject: life. "Life is worth living." But we can also just say, "It's worth it." In this case, we use a sort of prop word, the particle ne.

We use ne when we comment on something being worth it or not. We know what we're talking about, but we don't need to repeat it. So we use ne.

Here's the negative version:

[Qualcosa] non vale la pena ([something] is not worth it).

Non ne vale la pena (it's not worth it).

We can say the same exact thing as a question: Here too, we'll use the particle ne if we don't include the subject (the thing that isn't worth it).

Vale la pena (is [something] worth it/worth the trouble)?

Ne vale la pena (is it worth it)?

The third way we use valere is to say something is applicable.

Questa regola vale soltanto per il singolare,

This rule applies only to the singular,

quando io parlo della mia famiglia in singolare.

when I talk about my family in the singular.

Captions 14-15, Corso di italiano con Daniela - Aggettivi Possessivi

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Vale la pena studiare l'italiano? Speriamo di sì!

Although we can sometimes use the noun il turno to mean "the turn," as in, "Wait your turn" (aspetta il tuo turno), there's another (colloquial) expression we use in Italian, more often than not. We use the verb toccare (to touch). In the following clip, Dino and Melody are making wishes with blueberries:

Adesso tocca a te.

Now it's your turn.

Caption 9, Sposami - EP 2 - Part 20

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Tocca a te (it's your turn).
Tocca a me (it's my turn). 

The question you might get in a shop where various people are waiting their turns:

A chi tocca (whose turn is it)?

The answer can be tocca a me, tocca alla signora, tocca a lei, tocca a loro...

Twisting this expression a bit turns it into something you have to do.

Mi tocca (I have to do it).
Ti tocca (you have to do it).

Ho faticato tanto per averla,

I worked so hard to get it,

e adesso mi tocca venderla.

and now I have to sell it.

Captions 6-7, Il Commissario Manara - S2EP10 -La verità nascosta

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The important thing to remember in using this expression is that the person is the indirect object. The preposition of choice is a (to, at). The subject is a general "it," implied, or absent, actually.

In some places, you take a number and then wait your turn, at the supermarket, for example, at the bread counter, or the counter where you get prosciutto. Otherwise, you can ask, Chi è l'ultimo (who's the last [in line])?