Hon sköljer jordgubbarna snabbt och lägger dem i en skål.

Because -na is the definite plural ending.

Here is the pattern:

• en jordgubbe = a strawberry
• jordgubben = the strawberry
• jordgubbar = strawberries
• jordgubbarna = the strawberries

So jordgubbarna means the strawberries, not just strawberries.

Sköljer is the present tense of skölja, and it usually means rinses or washes off with water.

In this sentence, it is a very natural verb because you often rinse fruit before eating it.

Compare:

• skölja = to rinse
• tvätta = to wash

For food like strawberries, skölja is usually the better choice.

Because dem is the object form.

In this part:

• lägger dem i en skål = puts them in a bowl

the strawberries are receiving the action, so Swedish uses the object pronoun dem.

A quick comparison:

• de = they
• dem = them

So:

• De lägger jordgubbarna i en skål = They put the strawberries in a bowl
• Hon lägger dem i en skål = She puts them in a bowl

Because lägger is the present tense, while lägga is the infinitive.

Here the sentence is describing what she is doing now, so Swedish uses present tense for both verbs:

• sköljer = rinses
• lägger = puts

The infinitive would be used in a different structure, for example:

• Hon vill lägga dem i en skål = She wants to put them in a bowl

Because the same subject continues after och.

Swedish often leaves out the repeated subject when two verbs share the same subject:

• Hon sköljer jordgubbarna snabbt och lägger dem i en skål

This is understood as:

• Hon sköljer jordgubbarna snabbt och hon lägger dem i en skål

But repeating hon is usually less natural here.

Because snabbt is the adverb form, meaning quickly.

• snabb = quick, fast
• snabbt = quickly, fast

In this sentence, the word describes the verb sköljer, not a noun, so an adverb is needed:

• Hon sköljer jordgubbarna snabbt = She rinses the strawberries quickly

Yes, sometimes Swedish allows some flexibility with adverb placement.

For example:

• Hon sköljer jordgubbarna snabbt
• Hon sköljer snabbt jordgubbarna

Both are possible, but the first version sounds very natural in this context.

The placement can slightly change emphasis, but the basic meaning stays the same.

Because skål is a common-gender noun, so it takes en in the indefinite singular.

• en skål = a bowl
• skålen = the bowl

In this sentence, it is a bowl, not the bowl, so Swedish uses the indefinite form:

• i en skål = in a bowl

In everyday speech, many speakers pronounce both de and dem as dom.

So although the sentence is written:

• lägger dem i en skål

it is often pronounced roughly like:

• lägger dom i en skål

In careful writing, though, the distinction between de and dem is still important.