Мы увидели грузовик.

• Мы = we; this is the subject.
• увидели = saw; this is the verb, in the past tense.
• грузовик = truck; this is the direct object, the thing that was seen.

So the structure is basically:

subject + verb + object
= We saw a truck

Because увидеть is the perfective verb, while видеть is imperfective.

In this sentence, увидели presents the action as one completed event: we caught sight of a truck.

Very roughly:

• мы увидели грузовик = we saw / caught sight of a truck as a complete event
• мы видели грузовик = can mean we saw a truck too, but with a more imperfective viewpoint: the fact of seeing it, repeated seeing, or seeing without focusing on the completed moment

So увидели is very natural when you mean a single finished action.

Russian past tense is usually formed with a -л- element plus endings.

In увидели, you can think of it like this:

• увиде-л-и

The important parts are:

• -л- = past tense marker
• -и = plural

So увидели means saw with a plural subject: we/you(pl.)/they saw.

Here the subject мы tells you it means we saw.

It helps form the perfective verb увидеть from видеть.

For learners, the most useful way to understand it is:

• видеть = to see
• увидеть = to see / catch sight of / come to see, with a completed-event meaning

It is not always helpful to translate the prefix у- by itself. In this verb, it is better to learn увидеть as a whole vocabulary item paired with видеть.

Because грузовик is an inanimate masculine noun, and in Russian the accusative singular of many inanimate masculine nouns is the same as the nominative singular.

Since грузовик is the direct object, it is in the accusative case. But for this kind of noun, the form does not change:

• nominative: грузовик
• accusative: грузовик

So the case is accusative here, even though the form looks unchanged.

Compare:

• Мы увидели грузовик. = inanimate, so no change
• Мы увидели брата. = animate, so the accusative changes

Мы is in the nominative case, because it is the subject of the sentence.

Russian subjects are normally in the nominative:

• я
• ты
• он / она / оно
• мы
• вы
• они

So in this sentence:

• мы = nominative subject
• грузовик = accusative object

Not always, but it is often useful.

Russian often drops pronouns when the meaning is clear from context. However, in the past plural, the verb form увидели by itself does not tell you the person:

• we saw
• you all saw
• they saw

All of those use the same past plural verb form.

So мы is helpful because it makes the subject explicit:

• Мы увидели грузовик. = We saw a truck.

If you just say Увидели грузовик, the subject would have to be understood from context.

Yes. Russian word order is much more flexible than English word order.

The neutral order here is:

• Мы увидели грузовик.

But other orders are possible, with different emphasis:

• Грузовик мы увидели. = emphasizes truck
• Увидели мы грузовик. = more marked or stylistic, depending on context

So the basic meaning can stay the same, but the focus or emphasis changes.

A helpful stressed version is:

Мы уви́дели грузови́к.

Approximate pronunciation:

• Мы = mɨ
• уви́дели = roughly oo-VEE-de-lee
• грузови́к = roughly groo-zuh-VEEK

A few notes:

• ы in мы has no exact English equivalent.
• In грузовик, the unstressed о sounds reduced, closer to uh than a clear English o.
• The stress is important: уви́дели, грузови́к.

Because Russian has no articles.

So грузовик can mean:

• a truck
• the truck

Context tells you which one is meant.

In this sentence, English will often use a truck if it is being mentioned for the first time:

• Мы увидели грузовик. = We saw a truck.

But Russian itself does not mark that distinction with an article.

The dictionary form is увидеть.

That is the infinitive, meaning to see in the perfective sense.

So:

• увидеть = infinitive
• увидели = past plural form

If you look it up in a dictionary, you would search for увидеть, not увидели.

Sometimes, depending on context.

Russian does not have a separate tense that matches the English present perfect exactly. A Russian past-tense form like увидели can often be translated as:

• we saw
• or, in the right context, we have seen

But the most straightforward translation of Мы увидели грузовик is usually We saw a truck or We caught sight of a truck.

So yes, English have seen can sometimes be possible in context, but the Russian form itself is simply past tense perfective.