Новая грамматическая тема: союз «то есть» помогает уточнять мысль: завтра я поеду на электричке, то есть на пригородном поезде.

Here то есть introduces a clarification. The speaker first says на электричке and then explains it more clearly with на пригородном поезде.

In English, it is often like that is, i.e., or in other words.

For practical purposes, treat то есть as a fixed expression.

Historically, it is connected to the idea of that is, but in modern Russian learners usually just memorize it as one unit meaning that is / namely / in other words. It does not change form.

In Russian school grammar, то есть is usually called a союз, meaning a conjunction or linking word.

Its job is to connect:

• the first statement
• the explanation or restatement that follows

So in на электричке, то есть на пригородном поезде, the second part explains the first part.

Because то есть introduces an explanatory insertion, it is normally set off by punctuation.

In this sentence, the clarification comes at the end, so you see a comma before it:

завтра я поеду на электричке, то есть на пригородном поезде

If the clarification were in the middle of a sentence, it could be surrounded by commas on both sides.

Поеду is the future form of поехать, and it is used for a single trip in the future: tomorrow I will go / I will set off.

Compare:

• я еду = I am going / I’m on my way now
• я поеду = I will go later, as a future trip
• я буду ехать = I will be going / I will be in the process of going

So завтра я поеду is the natural choice for a planned trip tomorrow.

With many means of transport, Russian uses на + prepositional case.

So:

• на электричке
• на поезде
• на автобусе
• на трамвае

In your sentence:

• электричке is prepositional singular
• пригородном поезде is also prepositional singular
• the adjective пригородном agrees with поезде

This is a common Russian pattern for saying by train / by bus / by tram, etc.

Yes, in this sentence repeating на is the natural and correct choice.

You are not just replacing one noun with another in isolation; you are clarifying the whole phrase:

• на электричке
• то есть на пригородном поезде

So the preposition is repeated because the second phrase is a full restatement of the first one.

Электричка is the everyday word Russians commonly use for a suburban or commuter train, especially the familiar local trains around cities.

Пригородный поезд is more formal and more general. It literally means suburban train.

In everyday life, these often refer to the same thing, which is why the sentence can use то есть to clarify one with the other. Technically, though, электричка has a slightly more specific, everyday feel.

Yes. In writing, it is often abbreviated as т. е.

For example: Я поеду на электричке, т. е. на пригородном поезде.

In learner materials and careful explanation, the full form то есть is often preferred because it is easier to recognize.

The colon is there because the text is introducing an example.

First it says the grammar point: союз то есть помогает уточнять мысль

Then after the colon it gives the example: завтра я поеду на электричке, то есть на пригородном поезде

So the colon is not part of the example sentence itself; it is just punctuation introducing the example.