Du brauchst vor der Abfahrt nur noch die Adresse ins Navi einzugeben.

Because this sentence uses the structure brauchen + zu + infinitive.

With a normal infinitive, you would say:

• Du brauchst die Adresse einzugeben.

But eingeben is a separable verb (ein-geben). In the zu-infinitive, zu goes between the prefix and the verb stem:

• eingeben → einzugeben

So:

• einzugeben = to enter / to type in

This is exactly parallel to other separable verbs:

• anzurufen from anrufen
• mitzubringen from mitbringen
• aufzumachen from aufmachen

So einzugeben already contains the zu.

Here brauchen means something like need to or have to, often in a limited sense such as only need to.

So:

• Du brauchst ... die Adresse ins Navi einzugeben.

means roughly:

• You only need to enter the address into the satnav.

A very common pattern is:

• brauchen + zu-infinitive

Examples:

• Du brauchst nicht zu kommen. = You don’t need to come.
• Ich brauche nur noch zu unterschreiben. = I only still need to sign.

In everyday German, many learners first meet brauchen mostly in negative sentences like nicht brauchen (don’t need to), but it can also appear with words like nur.

Nur noch is a very common combination and means something like:

• only now / only still / all that remains is

In this sentence, it suggests that most of the preparation is already done, and this is the last remaining step.

So:

• Du brauchst vor der Abfahrt nur noch die Adresse ins Navi einzugeben.

has the feeling of:

• Before leaving, the only thing you still need to do is enter the address into the satnav.

Compare:

• Ich muss nur noch meine Schuhe anziehen.
  = I only still need to put on my shoes.
• Wir brauchen nur noch zu bezahlen.
  = We only still need to pay.

Because vor here is being used in a time expression, and with time it takes the dative.

• vor der Abfahrt = before departure / before setting off

The noun is die Abfahrt, so in the dative singular it becomes:

• der Abfahrt

This is not about physical movement toward something. It is simply a time phrase.

Other examples:

• vor dem Essen = before the meal / before eating
• vor der Prüfung = before the exam
• vor dem Urlaub = before the vacation

So vor der Abfahrt is the normal form.

Abfahrt literally means departure.

In this sentence, it refers to the moment when you set off or leave. So:

• vor der Abfahrt = before departure / before you leave

Be aware that Abfahrt can also mean other things depending on context, for example:

• a train departure
• an exit off a road or motorway
• a ski run

But here it clearly means setting off / leaving.

Ins is a contraction of:

• in das → ins

So:

• ins Navi = into the satnav / into the navigation device

German often uses in with devices, screens, systems, or apps when you are entering information into them.

Examples:

• etwas ins Handy eingeben = enter something into the phone
• etwas in den Computer tippen = type something into the computer
• etwas ins System eintragen = enter something into the system

Even though in English you might think of this more abstractly, German treats it very naturally as putting information into a device or system.

Because in can take either the accusative or the dative, depending on the meaning.

Here the idea is directional: you are entering the address into the satnav. That triggers the accusative:

• ins Navi = in das Navi (accusative)

If you were talking about a location, you would use the dative:

• im Navi = in dem Navi = in the satnav

Compare:

• Ich gebe die Adresse ins Navi ein.
  = I enter the address into the satnav.
• Die Adresse steht schon im Navi.
  = The address is already in the satnav.

So the choice depends on direction/change versus location.

Because die Adresse is the direct object of eingeben.

You are entering what?

• die Adresse

Since Adresse is feminine, the nominative and accusative singular both look the same:

• nominative: die Adresse
• accusative: die Adresse

So the form does not change, but grammatically it is accusative.

Navi is short for Navigationsgerät or sometimes just used for a navigation system/app in general.

It is very common in everyday German and usually means:

• satnav
• GPS
• navigation device

So ins Navi eingeben means:

• to enter it into the satnav / GPS

It is informal and completely normal in spoken German.

The sentence follows the normal pattern for a German main clause with an infinitive construction.

1. The conjugated verb is in second position

• Du brauchst ...

2. Other information comes in the middle

• vor der Abfahrt
• nur noch
• die Adresse
• ins Navi

3. The infinitive goes to the end

• einzugeben

So the basic frame is:

• Du brauchst ... einzugeben.

with the other elements placed between the finite verb and the final infinitive.

A simpler version would be:

• Du brauchst die Adresse einzugeben.

Then the sentence expands by adding time and other details.

Yes, it is understandable and natural, though many speakers might more often say something like:

• Du brauchst vor der Abfahrt nur noch die Adresse ins Navi einzugeben.
• Du musst vor der Abfahrt nur noch die Adresse ins Navi eingeben.

The version with brauchen + zu-infinitive can sound slightly more like all you need to do is..., while müssen is often more direct.

So the original sentence is fine, but a learner should know that müssen is often the more straightforward alternative.

Yes. Ins is just the contracted form of in das.

So these mean the same thing:

• die Adresse ins Navi eingeben
• die Adresse in das Navi eingeben

In normal spoken and written German, ins is much more natural here.

Because du is the informal singular word for you.

So this sentence is addressed to one person in an informal situation.

If you wanted the formal version, it would be:

• Sie brauchen vor der Abfahrt nur noch die Adresse ins Navi einzugeben.

If you wanted the plural informal version, it would be:

• Ihr braucht vor der Abfahrt nur noch die Adresse ins Navi einzugeben.

So du tells you something about the relationship between speaker and listener, not about the basic grammar of the sentence.