На даче мы открыли банку тунца и сделали салат с яйцом.

На даче means at the dacha / at the country house.

A дача is a summer house or country cottage, a very common cultural idea in Russian. Russian often uses на with places that English would express with at or sometimes in.

So:

• на даче = at the dacha
• compare:
  • на работе = at work
  • на почте = at the post office

It is just the normal preposition used with this noun in this meaning.

Because after на when talking about location, Russian usually uses the prepositional case.

• dictionary form: дача
• prepositional singular: даче

So:

• дача = dacha
• на даче = at the dacha

This is a very common pattern:

• в доме = in the house
• на улице = on the street
• на даче = at the dacha

Because банку is the accusative singular form of банка.

The verb открыть means to open, and the thing being opened is the direct object, so it goes in the accusative:

• банка = can, jar
• открыли банку = opened a can

Since банка is a feminine noun ending in -а, its accusative singular is usually -у:

• книга → книгу
• машина → машину
• банка → банку

Here тунца is in the genitive singular.

In Russian, when one noun describes the contents of another noun, the second noun is often put in the genitive:

• банка тунца = a can of tuna
• compare:
  • чашка чая = a cup of tea
  • бутылка воды = a bottle of water

The dictionary form is тунец. Its genitive singular is тунца.

So the structure is:

• банку тунца = a can of tuna

Yes, you could, but it is slightly different in feel.

• банка тунца = a can of tuna
  This is the most natural way to name the food item itself.
• банка с тунцом = a can with tuna in it
  This sounds a bit more literal, focusing on the container and what is inside.

In everyday speech about food, банка тунца is very natural.

They are past tense plural forms, because the subject is мы = we.

Russian past tense agrees with the subject in gender/number:

• я открыл / открыла
• он открыл
• она открыла
• они открыли
• мы открыли

The same is true for сделали.

So:

• мы открыли = we opened
• мы сделали = we made

Because the sentence describes completed actions.

• открыли = opened, finished opening
• сделали = made, finished making

This fits the idea of a sequence of completed events:

1. we opened the can
2. we made the salad

If you used the imperfective forms:

• открывали
• делали

that would sound more like repeated action, process, background activity, or an unfinished viewpoint, depending on context.

So in a simple story about what happened, the perfective forms are the normal choice.

Russian often uses the singular after с when naming an ingredient in a general way.

So:

• салат с яйцом = salad with egg

This does not necessarily mean there was only one egg. It can simply describe the type of salad or one of its ingredients.

If you say с яйцами, that is also possible, but it sounds a bit more explicitly plural: with eggs.

In food descriptions, singular is often very natural:

• бутерброд с сыром
• пирожок с мясом
• салат с яйцом

Because the preposition с meaning with usually requires the instrumental case.

• dictionary form: яйцо
• instrumental singular: яйцом

So:

• с яйцом = with egg

Other examples:

• с сыром = with cheese
• с мясом = with meat
• с другом = with a friend

Yes. Russian often omits subject pronouns when they are clear from the verb form or from context.

So both are possible:

• Мы открыли банку тунца и сделали салат с яйцом.
• Открыли банку тунца и сделали салат с яйцом.

Including мы makes the subject a bit more explicit. Omitting it can sound more natural in connected speech when it is already obvious who did the action.

No, Russian word order is fairly flexible.

The given sentence is neutral and natural:

• На даче мы открыли банку тунца и сделали салат с яйцом.

But other orders are also possible, depending on emphasis:

• Мы на даче открыли банку тунца и сделали салат с яйцом.
• Банку тунца мы открыли на даче и сделали салат с яйцом.

The basic meaning stays the same, but the focus can shift. Russian word order often reflects what is already known and what is being emphasized.

Russian has no articles.

So банку тунца can mean:

• a can of tuna
• the can of tuna

and салат can mean:

• a salad
• the salad

Which meaning is intended depends on context.

English learners often look for an exact equivalent of a/the, but Russian simply does not mark that distinction with articles.

It mainly means and, but in this sentence it naturally connects two actions in sequence:

• открыли банку тунца
• и сделали салат с яйцом

Because both verbs are perfective past forms, the sentence strongly suggests a completed sequence of events: first one action happened, then the next.

So и is just and, but the overall grammar makes the sentence feel like a short narrative of what happened.