Дети любят мастерить вечером: один делает рамку из картона, а другая лепит из пластилина.

Because Russian commonly uses любить + infinitive to mean to like/love doing something.

• Дети любят мастерить = The children like making/crafting things
• Compare:
  • Я люблю читать = I like to read
  • Он любит готовить = He likes to cook

So любят is the finite verb (they like), and мастерить stays in the infinitive (to make/craft).

Мастерить usually means to make something by hand, to tinker, to craft, or to build small things, often in a practical or creative way.

Делать is much broader and more general: to do or to make.

In this sentence:

• Дети любят мастерить = they enjoy crafting / making things by hand in general
• один делает рамку = one of them is making a frame

So:

• мастерить describes the general hobby or activity
• делает describes one specific action: making a frame

Russian often uses certain time expressions in the instrumental case without a preposition.

So:

• утром = in the morning
• днём = during the day
• вечером = in the evening
• ночью = at night

That is why Russian says:

• Дети любят мастерить вечером

rather than something like в вечером, which would be incorrect.

Вечером is the instrumental singular of вечер.

Here the instrumental is used adverbially to express time: in the evening.

This is a fixed and very common pattern in Russian. A learner should treat these as standard time expressions:

• утро → утром
• вечер → вечером
• день → днём
• ночь → ночью

This structure means something like:

• one is making..., while another is sculpting...
• one..., and another...

Russian often uses один ..., а другой/другая ... to contrast or distribute actions between different people.

Here а is important. It is not exactly the same as and. It often means while, whereas, or and on the other hand.

So the sentence presents two different children doing two different things.

Because другая is feminine, while один is masculine.

This suggests the sentence is talking about:

• one boy making a frame
• another girl modeling with plasticine

Russian adjectives and pronouns must agree in gender with the person they refer to.

So:

• один = masculine
• одна = feminine
• другой = masculine
• другая = feminine

The noun itself is omitted, but understood from context.

An implied noun is omitted because Russian often leaves out words that are clear from context.

Here it could be understood as something like:

• один ребёнок делает рамку...
• другая девочка лепит...

or more naturally in English:

• one child is making a frame, and another is modeling with plasticine

The exact hidden noun is less important than the agreement:

• один refers to a male child
• другая refers to a female child

Because рамку is the accusative singular of рамка.

Рамка is the direct object of делает:

• делает что? → рамку

Since рамка is a feminine noun ending in -а, its accusative singular changes to -у:

• nominative: рамка
• accusative: рамку

This is a very common pattern:

• книга → книгу
• машина → машину
• рамка → рамку

Because after из meaning out of / made of / from, Russian normally uses the genitive case.

So:

• из картона = out of cardboard / from cardboard
• из пластилина = out of plasticine

Base forms:

• картон → картона
• пластилин → пластилина

This is a very common pattern:

• из дерева = from wood
• из бумаги = from paper
• из металла = from metal

The verbs describe different kinds of making.

• делать = to make/do
• лепить = to model, sculpt, mold by shaping a soft material

So:

• делает рамку из картона = is making a frame out of cardboard
• лепит из пластилина = is modeling/sculpting something out of plasticine

Notice that the second part does not name the object being made. Russian can leave it unstated if it is not important or is obvious from context.

Because Russian does not always have to state the thing being made if the material or activity is enough.

So лепит из пластилина can mean:

• is modeling something out of plasticine
• is doing some plasticine modeling

The sentence focuses on the activity, not the exact object.

If you wanted, you could add an object:

• лепит фигурку из пластилина = is making a little figure out of plasticine

The colon introduces an explanation or a more detailed description of what comes before it.

So the structure is:

• The children like crafting in the evening: here is what they do...

Then the sentence gives examples:

• one makes a frame
• another models with plasticine

In English, a colon can work similarly.

Yes. Russian word order is flexible, though each version may sound slightly different in emphasis.

The given sentence is natural:

• Дети любят мастерить вечером

But you could also say:

• Вечером дети любят мастерить

This puts more emphasis on in the evening.

In Russian, word order often reflects emphasis, topic, and style more than strict grammar. The original version is clear and neutral.

These are imperfective forms.

That makes sense because the sentence describes:

• a general liking/habit (любят мастерить)
• ongoing or typical activities (делает, лепит)

Why imperfective?

• любить is normally used with an imperfective infinitive for liking an activity
• мастерить describes the process/activity
• делает and лепит describe what the children are engaged in, not completed results

If the sentence focused on completion, Russian might use perfective verbs instead, but that is not the point here.

Not necessarily. Although а is sometimes translated as but, here it is better understood as:

• while
• and
• whereas
• and another

So:

• один делает рамку из картона, а другая лепит из пластилина

means something like:

• one is making a cardboard frame, while another is modeling with plasticine

There is contrast, but not a strong contradiction. It is more like meanwhile / on the other hand than a strong but.