На улице шёл дождь, поэтому мы прыгали через скакалку и делали упражнения на турнике в зале.

Here на улице means outside or outdoors.

Russian often uses на улице for the general outdoor environment:

• На улице холодно = It’s cold outside.
• На улице шёл дождь = It was raining outside.

В улице is not used for this meaning. The preposition в usually means being inside something enclosed, while улица is thought of as an open public space, so Russian uses на.

That is a normal Russian idiom. The verb идти is commonly used with weather, especially precipitation:

• идёт дождь = it’s raining
• идёт снег = it’s snowing

So шёл дождь simply means it was raining or rain was falling. It does not sound strange to a Russian speaker.

Because the verb agrees with дождь, and дождь is masculine singular.

In the past tense, Russian verbs agree in gender and number:

• masculine: шёл
• feminine: шла
• neuter: шло
• plural: шли

So:

• дождь шёл
• буря шла if the subject were feminine
• облако шло if the subject were neuter

Russian usually uses the past tense of an imperfective verb for this.

So:

• шёл дождь = it was raining
• мы прыгали = we were jumping / we used to jump / we jumped repeatedly
• мы делали упражнения = we were doing exercises

Russian does not need a special form like English was doing. The sense of ongoing, repeated, or background action usually comes from the imperfective aspect plus context.

Because поэтому is connecting two clauses:

• На улице шёл дождь
• поэтому мы прыгали через скакалку и делали упражнения на турнике в зале

So the comma separates the cause and the result:

• cause: it was raining outside
• result: so we did indoor exercise

This is standard Russian punctuation.

Because the subject is мы = we.

In the Russian past tense, plural subjects take plural verb forms:

• я делал / делала
• он делал
• она делала
• мы делали

So:

• мы прыгали
• мы делали

Скакалка means jump rope or skipping rope.

The phrase прыгать через скакалку literally means to jump over a rope, but in normal English it is just to jump rope or to skip rope.

Russian also has other natural expressions, such as:

• прыгать на скакалке
• скакать на скакалке

But прыгать через скакалку is perfectly understandable and natural. It emphasizes the idea of jumping over the rope as it passes under you.

Because через normally takes the accusative case, and скакалка is a feminine noun.

So:

• nominative: скакалка
• accusative: скакалку

Compare:

• через дорогу = across the road
• через мост = across the bridge
• через скакалку = over the jump rope

Турник is a horizontal bar or pull-up bar used for exercise.

So упражнения на турнике means exercises done on that bar, such as pull-ups or other bar exercises.

This is a very common word in Russian when talking about fitness, school sports grounds, or outdoor workout areas.

Because the two prepositions express different kinds of location.

• на турнике = on the bar / using the bar
  Russian uses на with things seen as surfaces, platforms, or apparatuses.

• в зале = in the hall / in the gym
  Russian uses в for being inside an enclosed space.

Both are in the prepositional case here:

• на турнике
• в зале

Most likely, yes.

Зал can mean:

• hall
• large room
• gym
• sports hall
• exercise room

In this sentence, because the people are doing physical activities, в зале most likely means in the gym, in the sports hall, or indoors in an exercise room.

Most naturally, it applies to both activities.

So the idea is: because it was raining outside, they were indoors, where they:

• jumped rope
• did exercises on the bar

Russian often places a location phrase near the end even if it covers more than one action. If someone wanted to make that even clearer, they could move в зале earlier, but the original sentence is normal.

Делать упражнения is a very common collocation meaning to do exercises.

It is a bit more specific than тренироваться:

• тренироваться = to train, to work out
• делать упражнения = to do exercises

So делали упражнения на турнике focuses on the actual exercise movements, not just the general idea of training.

Yes. Russian word order is flexible, although different orders can sound more or less natural depending on emphasis.

The original sentence is very natural because it goes:

1. situation/background
2. result

Another possible order:

• На улице шёл дождь, поэтому в зале мы прыгали через скакалку и делали упражнения на турнике.

That puts more emphasis on в зале.

So the original word order is not the only possible one, but it is a good, neutral choice.