Друг помог нам в беде.

Because the verb помочь / помогать (to help) takes the dative case in Russian, not the accusative.

• нам = to us / for us (dative)
• нас = us (accusative or genitive)

So:

• Друг помог нам = A friend helped us

This is different from English, where help takes a direct object.

Помог is the perfective past form of помочь, and it usually means the help is seen as a completed action.

• помог = helped / did help successfully
• помогал = was helping, used to help, or helped with focus on the process rather than completion

In Друг помог нам в беде, the idea is that the friend actually came through and helped at that moment of need, so помог fits well.

In the past tense, Russian verbs show gender and number.

• помог = masculine singular
• помогла = feminine singular
• помогло = neuter singular
• помогли = plural

So помог tells us the subject is masculine singular. That matches друг (friend, masculine).

Because after в when it means in a state or location, Russian often uses the prepositional case.

• беда = dictionary form, nominative
• в беде = in trouble / in difficulty

This is a fixed and very common expression:

• быть в беде = to be in trouble
• помочь в беде = to help in trouble / when someone is in trouble

So в беде is best understood as an idiomatic phrase meaning in trouble or in a difficult situation.

It can be quite general. Беда can mean trouble, misfortune, distress, or serious difficulty.

So Друг помог нам в беде can mean:

• the friend helped us when we were in trouble
• the friend helped us in a difficult situation
• the friend stood by us in our time of need

It does not have to mean a dramatic catastrophe; it can be broader than that.

Russian has no articles, so друг can mean:

• a friend
• the friend
• sometimes just friend in a general sense

Which one sounds best depends on context. English requires an article, but Russian does not.

Yes. Russian word order is more flexible than English because case endings show the grammatical roles.

For example:

• Друг помог нам в беде. = neutral, straightforward
• Нам помог друг. = emphasizes us
• В беде нам помог друг. = emphasizes the situation in trouble
• Друг нам помог в беде. = can emphasize the fact that it was the friend who helped

The basic meaning stays similar, but the focus changes.

Grammatically, yes: друг is a masculine noun, and the verb помог is also masculine.

So this sentence refers to a male friend. If it were a female friend, Russian would say:

• Подруга помогла нам в беде.

Usually друг means a real friend, not just an acquaintance. In many contexts, it can sound a bit stronger than casual English friend.

Russian also has:

• приятель = pal, buddy, acquaintance-like friend
• знакомый = acquaintance

So друг помог нам в беде can carry a sense of genuine loyalty.

A helpful pronunciation guide is:

Droog pa-MOG nam v bee-DYE

Approximate stress:

• друг
• помо́г
• нам
• в беде́

The stressed syllables are:

• помо́г
• беде́

That final stress in беде́ is important.