Tränaren berättar historien.

Because tränaren is the definite singular form of tränare.

• tränare = a trainer / a coach
• tränaren = the trainer / the coach

In Swedish, definiteness is often shown by adding an ending to the noun instead of using a separate word like the.

For the same reason: historien is the definite singular form.

• historia = a story / a history
• historien = the story / the history

So the sentence uses two definite nouns:

• tränaren = the coach
• historien = the story

It is built into the nouns themselves.

Swedish often puts the definite marker at the end of the noun:

• tränare → tränaren
• historia → historien

So English uses a separate word, but Swedish often uses a suffix.

Berättar is the present tense of berätta.

• berätta = to tell
• berättar = tells / is telling

In a sentence like this, English might translate it as either:

• The coach tells the story
• The coach is telling the story

The exact choice depends on context.

Because Swedish verbs do not change for different persons the way English verbs sometimes do.

For example, Swedish uses the same present-tense form with different subjects:

• jag berättar = I tell / am telling
• du berättar = you tell / are telling
• tränaren berättar = the coach tells / is telling

So you do not need a special verb ending for he/she/it like English tells.

This is the normal Swedish subject–verb–object order:

• Tränaren = subject
• berättar = verb
• historien = object

So it is directly parallel to English:

• The coach tells the story

This is the most basic and common word order in Swedish main clauses.

Yes. Tränare can mean trainer or coach, depending on context.

For example:

• in sports, tränaren often means the coach
• in fitness or other settings, it may mean the trainer

So the best translation depends on the situation.

Not exactly. Berätta usually means tell, narrate, or relate something.

So:

• berätta en historia = tell a story
• säga = say

A useful contrast:

• Han säger något. = He says something.
• Han berättar en historia. = He tells a story.

So in this sentence, berättar is a very natural verb because the object is historien.

A rough guide is:

TREH-na-ren beh-RETT-ar hi-STO-ree-en

A few helpful points:

• ä is somewhat like the e in bed
• tt in berättar is a clear double consonant
• historien has several syllables, and the stress is on sto

A more natural pronunciation will come with listening practice, but that rough version is a good start.