On cierpi na ból pleców, więc dziś nie idzie do pracy.

Yes, Polish often drops subject pronouns because the verb form usually already shows who is doing the action.

• On cierpi... = He suffers...
• Cierpi... can also mean He suffers... if the context is clear.

Here, on may be included for clarity, emphasis, or because this is a learner example. In natural speech, both are possible:

• On cierpi na ból pleców.
• Cierpi na ból pleców.

The verb cierpieć often combines with na when talking about illnesses, conditions, or ailments.

So:

• cierpieć na grypę = to suffer from the flu
• cierpieć na astmę = to suffer from asthma
• cierpieć na ból pleców = to suffer from back pain

In this pattern, na is just the preposition required by the expression. It does not translate word-for-word very neatly; you should learn cierpieć na as a set phrase meaning to suffer from.

Ból pleców is the normal Polish way to say back pain.

Here is how it works:

• ból = pain
• plecy = back

Even though plecy looks plural, it is the normal Polish word for back in the anatomical sense. It behaves like a plural noun.

After a noun like ból you often get another noun in the genitive:

• ból głowy = headache
• ból zęba = toothache
• ból pleców = back pain

So pleców is the genitive plural form of plecy.

This is just a difference between the two languages. In Polish, plecy is normally a plural-only noun for back.

That means you say:

• bolą mnie plecy = my back hurts
• ból pleców = back pain

You do not normally use a singular form the way English does. This is something learners simply need to memorize.

Więc means so, therefore, or thus.

In this sentence:

• On cierpi na ból pleców, więc dziś nie idzie do pracy.
• He has back pain, so today he isn’t going to work.

It connects cause and result.

Compare:

• więc = so
• dlatego = therefore / for that reason

Both can work in similar contexts, though the sentence structure may change a bit:

• Cierpi na ból pleców, więc dziś nie idzie do pracy.
• Cierpi na ból pleców, dlatego dziś nie idzie do pracy.

Both are correct here.

Polish often uses the present tense to talk about a planned or expected future action, especially with motion verbs.

So:

• dziś nie idzie do pracy literally looks like today he is not going to work
• but in context it means today he isn’t going to work / he’s not going to work today

This is very natural in Polish, just like English can say:

• I’m not going to work tomorrow instead of
• I will not go to work tomorrow

This is an important Polish motion-verb distinction.

• iść = to go, one time, in one direction, a specific trip
• chodzić = to go habitually, repeatedly, or around on foot

Here, the sentence talks about today’s specific trip to work, so iść is the correct verb:

• dziś nie idzie do pracy = today he is not going to work

If you said:

• nie chodzi do pracy that would usually mean he doesn’t go to work (regularly) or he doesn’t have a job / doesn’t attend work, depending on context.

So the choice of idzie shows a one-time, specific event.

The preposition do often means to when talking about going to a destination.

• iść do pracy = to go to work
• iść do szkoły = to go to school
• iść do domu = to go home

After do, Polish uses the genitive case.

So:

• praca = work
• do pracy = to work

In Polish, negation is usually made by putting nie before the verb.

So:

• idzie = he goes / he is going
• nie idzie = he does not go / he is not going

This is the normal and basic way to make a verb negative.

Yes, but they are slightly different in style or emphasis.

• cierpi na ból pleców = he suffers from back pain
  This sounds a bit more formal or medical.
• ma ból pleców = he has back pain
  Understandable, but less idiomatic than some other options.
• bolą go plecy = his back hurts / his back is hurting
  Very natural in everyday speech.

A very common conversational version would be:

• Bolą go plecy, więc dziś nie idzie do pracy.

Yes, Polish word order is fairly flexible, because endings carry a lot of grammatical information.

The original order:

• On cierpi na ból pleców, więc dziś nie idzie do pracy.

This is neutral and clear.

Other orders are also possible:

• Dziś nie idzie do pracy, bo cierpi na ból pleców.
• Dziś on nie idzie do pracy, bo cierpi na ból pleców.

Changing the order usually changes emphasis, not the core meaning.

For example:

• dziś near the front emphasizes today
• on near the front emphasizes he

Not in exactly the same place with exactly the same meaning.

• więc means so, introducing a result
• bo means because, introducing a cause

So the original structure is:

• He has back pain, so he isn’t going to work today.

With bo, you would normally reverse the logic:

• Dziś nie idzie do pracy, bo cierpi na ból pleców.
• He isn’t going to work today because he has back pain.

Both sentences communicate nearly the same overall idea, but the connector changes the structure.

A rough guide:

• cierpi ≈ CHERP-ee
  The beginning cie- sounds somewhat like chye or che, depending on accent and speed.
• ból ≈ bool
  The ó sounds like u in modern Polish.
• dziś ≈ jeesh or dzhish, but softer
  The final ś is a soft sh sound.

A few useful pronunciation notes:

• ó = pronounced like u
• ś = a soft sh
• dz is a voiced sound, somewhat like the start of jam plus z, depending on the word

If you want to sound natural, it helps to listen to native recordings, especially for sounds like dziś and cierpi.