Heute haben wir viel Zeit, deshalb gehen wir in den Park.

Because German main clauses usually follow the verb-second rule.

That means:

• the finite verb must be in the second position
• whatever comes first can be the subject, a time word, a place word, an object, etc.

In this sentence, Heute is in the first position, so the verb haben must come next:

• Heute haben wir viel Zeit.

If the subject comes first instead, then the order is:

• Wir haben heute viel Zeit.

Both are correct, but the emphasis is slightly different.

Yes. In German, the first position is usually taken by one element, not necessarily one word in the English sense.

Here, Heute is a time adverb and it fills that first slot:

• Heute | haben | wir | viel Zeit

You could also put a longer phrase there, for example:

• Heute nach der Arbeit gehen wir in den Park.

That whole phrase can function as the first element.

Because the sentence contains two main clauses:

• Heute haben wir viel Zeit
• deshalb gehen wir in den Park

In German, main clauses are often separated by a comma when they are joined like this.

Also, deshalb is not a subordinating conjunction like weil. It is a conjunctive adverb or connecting adverb, so the second part still keeps normal main-clause word order.

Again, this is because of the verb-second rule in a main clause.

In the second clause, deshalb takes the first position, so the verb gehen must come second:

• deshalb gehen wir in den Park

This is the same pattern as:

• Heute haben wir viel Zeit
• Morgen fahren wir nach Berlin
• Dann essen wir

So after deshalb, the verb comes immediately.

They both relate to reason, but they work differently.

• deshalb = therefore / for that reason
• weil = because

The grammar changes too:

With deshalb, you have a main clause, so the verb stays in second position:

• Heute haben wir viel Zeit, deshalb gehen wir in den Park.

With weil, you introduce a subordinate clause, so the verb goes to the end:

• Wir gehen in den Park, weil wir heute viel Zeit haben.

So a learner often needs to remember:

• deshalb → verb second
• weil → verb at the end

Because in den Park gehen expresses movement toward/into the park.

German prepositions like in can take:

• accusative for direction/movement
• dative for location

So:

• Wir gehen in den Park. = we go into/to the park
• Wir sind im Park. = we are in the park

im Park is short for in dem Park, and it describes being located there, not going there.

Because Park is a masculine noun, and here it is in the accusative singular.

The article changes like this:

• nominative: der Park
• accusative: den Park

It becomes accusative because in is being used with a sense of movement:

• in den Park gehen

So the important combination is:

• masculine + accusative = den

Because viel often works like a quantity word with uncountable or abstract nouns.

So German commonly says:

• viel Zeit
• viel Geld
• viel Arbeit

This is similar to English:

• a lot of time
• a lot of money

You do not need an article here. Viel Zeit sounds completely natural.

Because German often uses the present tense to talk about the near future when the context is clear.

Here, the sentence means something like:

• we have time now, so we are going to the park

German very often prefers the simple present in this kind of situation:

• Morgen fahre ich nach Hamburg.
• Heute Abend bleiben wir zu Hause.

You could use werden for the future, but it is less natural here:

• Deshalb werden wir in den Park gehen.

That sounds more formal or more explicitly future-focused.

Yes, often you can, but the emphasis changes.

For example:

• Heute haben wir viel Zeit, deshalb gehen wir in den Park.
• Wir haben heute viel Zeit, deshalb gehen wir in den Park.
• Deshalb gehen wir heute in den Park.

All of these are possible in the right context.

German word order is flexible, but the finite verb in a main clause still stays in second position. That rule is the key thing to protect when you move parts around.

Because all nouns are capitalized in German.

So:

• der Park
• die Zeit

But heute is not normally capitalized unless it begins a sentence.

That means:

• Heute haben wir viel Zeit.
• Wir haben heute viel Zeit.

In the second version, heute is lowercase because it is not a noun and it is not at the start of the sentence.