Við setjum litlar plöntur í hjólbörurnar og berum þær að nýja beðinu.

The dictionary forms are:

• setja = to put / to place
• bera = to carry

In the sentence, both are in the 1st person plural present tense, because the subject is við = we.

So:

• við setjum = we put
• við berum = we carry

These forms are just the normal we forms of the verbs.
Bera is a very common verb and somewhat irregular, so berum may not look very close to the infinitive at first.

Because the adjective has to agree with the noun in:

• gender
• number
• case

Here:

• planta = plant is feminine
• plöntur = plants is plural
• it is the direct object of setjum, so it is in the accusative

So the adjective lítill = small/little becomes litlar to match plöntur.

So:

• litlar plöntur = small plants

A useful detail: for this noun phrase, the nominative plural and accusative plural happen to look the same, but in this sentence it is functioning as the accusative object.

This is the difference between strong and weak adjective forms in Icelandic.

• litlar plöntur is indefinite = small plants
• nýja beðinu is definite = the new bed

In Icelandic, adjectives are usually:

• strong with indefinite nouns
• weak with definite nouns

So:

• litlar plöntur = strong adjective form
• nýja beðinu = weak adjective form

That is why the adjective endings are different.

Because í can take two different cases depending on meaning:

• accusative for motion into
• dative for location in

Here the meaning is putting the plants into the wheelbarrows, so there is movement toward the inside of something. That is why Icelandic uses the accusative:

• í hjólbörurnar = into the wheelbarrows

If the sentence meant that the plants were already there, you would expect the dative:

• í hjólbörunum = in the wheelbarrows

This accusative/dative contrast with prepositions is very important in Icelandic.

Þær means them, and it refers back to litlar plöntur = small plants.

It has this form because it must match the noun it replaces:

• plöntur is feminine
• plural
• and here the pronoun is the direct object of berum, so it is accusative

So:

• þær = them referring to feminine plural nouns

That is why you do not get þá or þau here:

• þá would be masculine plural accusative
• þau would be neuter plural nominative/accusative

Because að and í do different jobs here.

• að + dative often means to / toward
• í + accusative means into

So:

• berum þær að nýja beðinu = we carry them to the new bed
• it does not necessarily mean the plants are placed into the bed yet

If you wanted to say into the new bed, you would expect something like:

• í nýja beðið

So the sentence describes:

1. putting the plants into the wheelbarrows
2. carrying them to the new bed

Because the preposition að normally takes the dative.

The noun is:

• beð = bed (a garden bed / flower bed)
• it is neuter singular

Its definite dative singular form is:

• beðinu = the bed

So:

• að nýja beðinu = to the new bed

The adjective nýja is also in the matching weak form for a definite neuter singular noun phrase.

In Icelandic, the is usually not a separate word like in English. Instead, it is usually added to the end of the noun.

So:

• hjólbörur = wheelbarrows
• hjólbörurnar = the wheelbarrows

and:

• beð = bed
• beðinu = the bed (here in the dative singular)

So the definite article is built into the noun itself.

Yes, in this sentence it is definitely plural:

• the ending -nar shows a definite plural form

So hjólbörurnar means the wheelbarrows.

A learner may notice that Icelandic often uses hjólbörur in plural-looking forms, and this word is commonly encountered that way. In this sentence, though, the grammar is clear: it means plural.

So the phrase is:

• í hjólbörurnar = into the wheelbarrows

not into the wheelbarrow.

Because Icelandic usually expresses the with an ending attached to the noun rather than with a separate article.

Examples from the sentence:

• hjólbörurnar = the wheelbarrows
• beðinu = the bed

So English uses:

• the wheelbarrows
• the bed

but Icelandic usually uses:

• noun + definite ending

This is one of the most noticeable differences between English and Icelandic noun phrases.