Věřím, že je to pravda.

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

• věřím already means I believe
• so já is not necessary

You could say Já věřím, že je to pravda, but that sounds more emphatic, like I believe it (maybe as a contrast with someone else).

Věřím is the 1st person singular present tense of the verb věřit.

So:

• věřit = to believe, to trust
• věřím = I believe / I trust

In this sentence, it means I believe in the sense of I believe that something is true.

That ending shows:

• present tense
• 1st person singular
• so, I ...

The present-tense forms of věřit are:

• věřím = I believe
• věříš = you believe
• věří = he/she/it believes
• věříme = we believe
• věříte = you believe
• věří = they believe

So the -ím ending is the form that matches I.

Yes. Věřit often takes the dative case when it has an object:

• věřím tomu = I believe that / I believe it
• věřím ti = I believe you
• věřím Bohu = I believe God / I trust God

So Věřím tomu, že je to pravda is also correct.

The version without tomu — Věřím, že je to pravda — is very natural and common. The tomu version is a little more explicit.

Že means that and introduces a subordinate clause.

So:

• Věřím = I believe
• že je to pravda = that it is true

Together: I believe that it is true.

Usually no.

In English, both are possible:

• I believe that it is true
• I believe it is true

But in Czech, že is normally kept. So:

• Věřím, že je to pravda. = correct
• Věřím, je to pravda. = not the normal way to say it

So this is an important difference from English.

Because Czech punctuation rules require a comma before a subordinate clause introduced by words like:

• že = that
• protože = because
• když = when
• aby = so that

So in Czech, the comma in Věřím, že je to pravda. is required.

This is different from English, where that often appears with no comma.

Literally, it is something like:

• je = is
• to = it / that
• pravda = truth

So, literally: it is truth or that is truth

But the natural English translation is simply:

• it is true
• or that's true, depending on context

Two things are happening here:

1. Pravda is a noun meaning truth.
   Czech often uses the expression je to pravda where English uses the adjective true.

2. Czech has no articles.
   There is no direct equivalent of a or the.

So pravda can mean truth, the truth, or just be part of the fixed expression je to pravda = it is true.

Actually, both are possible.

• že je to pravda
• že to je pravda

The version in your sentence, že je to pravda, is very natural and neutral.

If you say že to je pravda, the to can sound a little more highlighted. In many cases, the difference is small, but Czech word order often affects emphasis more than basic meaning.

They are similar, but not identical.

• věřím, že... = I believe that...
• myslím, že... = I think that...

Věřím often sounds a bit stronger, as if you accept something as true or have faith in it.

Myslím is more like giving an opinion.

So:

• Věřím, že je to pravda. = I believe it is true.
• Myslím, že je to pravda. = I think it is true.

The hardest part is usually ř, which is a special Czech sound.

A rough guide:

• vě sounds approximately like vye
• ř is a sound somewhere between r and the zh sound in measure
• -ím sounds like eem

So věřím can be approximated as vye-rzheem, though that is only an approximation.

Also remember that Czech word stress is usually on the first syllable:

• VĚ-řím

In the full sentence:

• VĚ-řím, že je to PRAV-da.