Vi orienterade oss med kompassen.

Orienterade is the past tense (preterite) of orientera.

So:

• orientera = to orient / to navigate / to find one’s bearings
• orienterade = oriented / navigated / found one’s bearings

In this sentence, it describes something we did in the past.

Oss is the reflexive/object pronoun meaning ourselves/us.

The verb here is really orientera sig, which is a reflexive verb in Swedish. That means it is commonly used together with a reflexive pronoun:

• jag orienterade mig = I oriented myself / I found my way
• du orienterade dig
• han/hon orienterade sig
• vi orienterade oss
• ni orienterade er
• de orienterade sig

So oss is there because the subject is vi and the reflexive pronoun has to match it.

Yes, literally it does. But in natural English, you would often translate it more idiomatically as:

• we got our bearings
• we navigated
• we found our way
• we used the compass to orient ourselves

So the Swedish expression can sound more natural than the literal English equivalent.

In this context, orientera sig means something like:

• to get one’s bearings
• to figure out one’s direction
• to navigate
• to determine where one is and which way to go

It does not necessarily mean formal sports orienteering, although it is related to the same idea of direction and navigation.

Med means with or using.

So med kompassen means:

• with the compass
• using the compass

It shows the instrument or tool used to do the action.

Compare:

• Jag skrev med en penna. = I wrote with a pen.
• Vi orienterade oss med kompassen. = We found our bearings using the compass.

Kompassen is the definite form: the compass.

• en kompass = a compass
• kompassen = the compass

Swedish often uses the definite form when talking about a specific object that is known from the situation or context. So this sentence suggests a particular compass that the speakers had or were using.

If you said med en kompass, that would mean with a compass, with less emphasis on a specific known one.

Grammatically, oss can be both:

• the ordinary object form of vi = us
• the reflexive form used with vi = ourselves

In this sentence, it is understood as reflexive, because orientera sig is the normal pattern.

So:

• Hon såg oss. = She saw us. → ordinary object
• Vi orienterade oss. = We oriented ourselves / got our bearings. → reflexive use

The verb tells you which meaning is intended.

Because sig is only used for third person reflexive subjects:

• han orienterade sig
• hon orienterade sig
• de orienterade sig

But with vi, Swedish uses oss:

• vi orienterade oss

So the reflexive pronoun changes depending on the subject.

This sentence has the normal main-clause word order in Swedish:

• Vi = subject
• orienterade = verb
• oss = reflexive pronoun/object
• med kompassen = adverbial phrase

So the structure is:

Subject + verb + reflexive pronoun + prepositional phrase

Nothing unusual is happening here.

Yes, you could, but the meaning is slightly different.

• Vi orienterade oss med kompassen emphasizes finding our bearings / figuring out direction
• Vi navigerade med kompassen emphasizes navigating more generally

Another simple alternative would be:

• Vi använde kompassen för att orientera oss. = We used the compass to orient ourselves.

So the original sentence is very natural if the focus is on working out direction with the help of the compass.

It is fairly common, especially in contexts involving:

• maps
• direction
• being lost
• hiking
• outdoor activities

The reflexive form orientera sig is especially useful and common when talking about getting oriented in a place or situation.

It can also be used more abstractly, for example:

• Jag behöver tid att orientera mig i den nya rollen.
  = I need time to get oriented in the new role.

So it can be both physical and figurative.

The present tense would be:

Vi orienterar oss med kompassen.

That means:

• We are orienting ourselves with the compass
• We use the compass to get our bearings

So:

• orienterar = present
• orienterade = past

A rough English-friendly approximation is:

or-ee-en-TEH-ra-de

But Swedish pronunciation is smoother than that, and the stress is mainly on -te-.

Also:

• orientera has four syllables
• orienterade has five syllables

If you are learning pronunciation, it helps to notice that Swedish often keeps the ending clearly audible in careful speech.