Ten stůl je tak těžký, že ho sama nemůžu odnést.

Because stůl is a masculine noun. In Czech, demonstratives have to agree with the noun’s gender, number, and case.

• ten = masculine singular
• ta = feminine singular
• to = neuter singular

So:

• ten stůl = that/this table
• ta židle = that/this chair
• to okno = that/this window

Since stůl is masculine, ten is the correct form.

Because the adjective has to agree with stůl.

Here, stůl is:

• masculine
• singular
• nominative

So the adjective also takes the matching form:

• těžký stůl = a heavy table

If the noun changed, the adjective would change too:

• těžká židle = a heavy chair
• těžké křeslo = a heavy armchair

In this sentence, těžký matches stůl.

tak ... že means so ... that.

So:

• tak těžký, že... = so heavy that...

This is a very common Czech structure:

• Je tak unavený, že usnul. = He is so tired that he fell asleep.
• Bylo tak horko, že jsme nešli ven. = It was so hot that we didn’t go outside.

In your sentence, tak těžký, že ho sama nemůžu odnést means the table is heavy to such a degree that the result is: I can’t carry it away by myself.

ho is the pronoun meaning him/it, here it, referring back to stůl.

It is in the accusative, because it is the direct object of odnést.

You are carrying what?
→ the table
So the table becomes the object, and the pronoun takes the accusative form.

For a masculine inanimate noun like stůl, the pronoun is still ho here.

So:

• Ten stůl... = That table...
• ...že ho... = ...that I can’t carry it...

Because ho is a short unstressed pronoun, and Czech usually puts these short forms very early in the clause, often in the second position.

After že, the clause is:

• ho sama nemůžu odnést

This order is natural because clitic-like short words such as ho, mi, ti, se, si tend to come near the beginning of the clause.

So although English says I can’t carry it away by myself, Czech naturally places ho earlier.

That is why že sama ho nemůžu odnést sounds less natural in ordinary usage.

sama means alone or by myself, and it agrees with the speaker.

The subject I is not stated explicitly, but it is understood from nemůžu.
Because the speaker is female, the form is sama.

If a male speaker said it, it would be:

• ...že ho sám nemůžu odnést.

So:

• sám = by myself, if the speaker is male
• sama = by myself, if the speaker is female

It adds the idea that the speaker cannot do it without help.

Because Czech often drops subject pronouns when they are already clear from the verb ending.

Here, nemůžu already tells you the subject is I:

• nemůžu = I cannot

So Czech usually does not need já unless you want emphasis or contrast.

Compare:

• Nemůžu ho odnést. = I can’t carry it away.
• Já ho nemůžu odnést. = I can’t carry it away.
  (maybe someone else can, but I can’t)

In your sentence, leaving out já is completely normal.

nemůžu means I can’t / I am not able to.

It comes from můžu = I can / I am able to, with ne- added for negation:

• můžu = I can
• nemůžu = I can’t

This form is very common in everyday Czech. A more formal or bookish variant is:

• nemohu

Both are correct standard Czech, but:

• nemůžu sounds more natural in normal speech
• nemohu sounds more formal, careful, or written

Because after verbs like můžu (can), Czech normally uses an infinitive.

So:

• můžu odnést = I can carry away
• nemůžu odnést = I can’t carry away

This works like English can + verb.

Examples:

• Můžu přijít. = I can come.
• Nemůžu spát. = I can’t sleep.
• Můžu to udělat. = I can do it.

nést means to carry / to bear.
odnést means to carry away, take away by carrying, or remove by carrying.

The prefix od- often adds the idea of away from somewhere.

So there is a difference:

• nést = carry
• odnést = carry away / take away

In this sentence, odnést suggests not just holding or carrying the table, but moving it away from its place.

Also, odnést is perfective, which often fits well when talking about completing an action:

• Nemůžu ho odnést. = I can’t carry it away / I can’t manage to take it away.

Because stůl and ho have different roles in the sentence.

In the first clause:

• Ten stůl je tak těžký
  Here stůl is the subject, so it is in the nominative.

In the second clause:

• že ho sama nemůžu odnést
  Here the table is no longer the subject; it is the object of odnést, so Czech uses the accusative pronoun ho.

So the same thing can appear in different forms depending on its grammatical role.

Yes, sometimes. Czech ten/ta/to does not map perfectly onto English this/that.

Depending on context, ten stůl can mean:

• that table
• this table
• sometimes even something close to the table

If Czech wants to be more explicitly like English this, speakers may use forms such as:

• tenhle stůl
• tento stůl

But plain ten stůl is very common and often natural.

So you should not assume ten always equals only that.

People would understand it, but že ho sama nemůžu odnést is more natural.

The reason is word order with short pronouns like ho. Czech tends to place them very early in the clause.

So the preferred order is:

• že ho sama nemůžu odnést

rather than:

• že sama ho nemůžu odnést

The second version is not impossible, but it sounds less neutral.

It can be omitted, but the meaning changes slightly.

• ...že ho nemůžu odnést.
  = ...that I can’t carry it away.

• ...že ho sama nemůžu odnést.
  = ...that I can’t carry it away by myself / alone.

So sama adds an important nuance: the speaker may be able to do it with help, but not alone.

Because že introduces a subordinate clause, and Czech punctuation normally separates that clause with a comma.

So the sentence is divided into:

• Ten stůl je tak těžký,
• že ho sama nemůžu odnést.

This is standard Czech punctuation, similar to how English often separates longer so...that structures in writing, though Czech is more consistent about it.

Only sama would change:

• Ten stůl je tak těžký, že ho sám nemůžu odnést.

That is because sám/sama agrees with the speaker’s gender.

Everything else stays the same.

Yes. It sounds natural and idiomatic.

A few points make it very everyday-sounding:

• nemůžu instead of more formal nemohu
• omission of já
• normal placement of ho
• use of sama for by myself

So this is a good model for real spoken or informal written Czech.