Det känns skönt att minska matsvinnet.

Here det is a dummy subject. It does not point to a specific thing like it often does in English.

In Swedish, sentences about weather, time, and general experiences often use det:

• Det regnar. = It is raining.
• Det är svårt. = It is difficult.
• Det känns skönt att minska matsvinnet. = It feels good/nice to reduce food waste.

So det is mainly there because Swedish usually wants a subject in the sentence.

Känns is the present tense of kännas, which means to feel, to seem, or to feel like in this kind of sentence.

So:

• Det känns skönt = It feels nice / It feels good

Even though the -s form often looks passive in Swedish, kännas is very commonly used as its own verb with this meaning. So here you should learn kännas as a normal expression:

• Det känns bra. = It feels good.
• Det känns konstigt. = It feels strange.

Because the adjective is agreeing with det, which is treated as neuter singular.

The basic adjective is:

• skön = nice, pleasant, comfortable

Its neuter form is:

• skönt

So:

• en skön dag = a nice day
• ett skönt bad = a nice bath
• Det känns skönt. = It feels nice.

In sentences with dummy det, Swedish usually uses the neuter adjective form.

It is an infinitive phrase meaning to reduce food waste.

The structure is:

• Det känns skönt = It feels good
• att minska matsvinnet = to reduce food waste

Together:

• Det känns skönt att minska matsvinnet.

So the att + infinitive phrase explains what feels good.

This is very common in Swedish:

• Det är roligt att lära sig svenska. = It is fun to learn Swedish.
• Det känns svårt att välja. = It feels hard to choose.

Yes. Minska can be used both intransitively and transitively.

• Intransitive: something decreases
  
  • Kostnaderna minskar. = The costs are decreasing.
• Transitive: someone reduces something
  
  • Vi minskar kostnaderna. = We are reducing the costs.

So in your sentence:

• minska matsvinnet = reduce food waste

That is perfectly normal Swedish.

Matsvinnet is the definite form of matsvinn.

• ett matsvinn = a food waste / food-waste amount (not very common in everyday use)
• matsvinnet = the food waste

In Swedish, the definite form is often used where English would use a more general noun without the. So even though English often says reduce food waste, Swedish very naturally says:

• minska matsvinnet

It refers to the food waste as a known issue/category, not necessarily one specific pile of wasted food.

Yes, it is one word, because Swedish forms compounds very freely.

It is built like this:

• mat = food
• svinn = waste, loss, shrinkage
• matsvinn = food waste
• matsvinnet = the food waste

So Swedish often combines words where English uses separate words:

• matbutik = food store / grocery store
• klimatförändring = climate change
• matsvinn = food waste

Also, matsvinn is an ett-word, so the definite form is matsvinnet.

Yes, absolutely.

Both are grammatical:

• Det känns skönt att minska matsvinnet.
• Att minska matsvinnet känns skönt.

The version with det is often more natural and common in everyday Swedish. The version with the infinitive phrase first can sound a little more formal, more written, or more focused on the activity itself.

So if you are unsure, Det känns skönt att ... is a very safe pattern to use.

Both can often be translated similarly, but there is a slight difference in feeling.

• Det känns skönt att ... = emphasizes the personal feeling or sensation
• Det är skönt att ... = can sound a bit more general or matter-of-fact

Compare:

• Det känns skönt att vara klar. = It feels good to be finished.
• Det är skönt att vara klar. = It is nice/good to be finished.

In many situations, both work. Känns often sounds a little more emotional or immediate.

It is present tense.

The verb forms are:

• infinitive: kännas
• present: känns
• past: kändes
• supine: känts

So:

• Det känns skönt. = It feels nice.
• Det kändes skönt. = It felt nice.
• Det har känts skönt. = It has felt nice.

A careful approximate pronunciation is:

deh chens shurnt at minska mat-svin-neh

A few useful points:

• Det is often pronounced more like deh in normal speech.
• känns sounds roughly like chens.
• skönt has a vowel sound English does not really have; the ö is like a rounded vowel.
• matsvinnet has the stress mainly on mat: MAT-svinnet.

You do not need perfect pronunciation right away, but it helps to notice that spoken Swedish is often a bit softer and more reduced than the spelling suggests.