Learn Dutch: De hond slaapt daar. - The dog sleeps there.

This is because of the Dutch spelling rules for open and closed syllables. In slapen (sla-pen), the first syllable ends in a vowel, making it an open syllable where a single a makes a long vowel sound. To make the present tense form for 'the dog', we take the verb stem (slaap) and add t. Because slaap ends in a consonant, it is a closed syllable. We must double the a to aa so it keeps that same long vowel sound. If we just wrote slapt, the vowel would become short.

I hear a 't' sound at the end of hond, but it is spelled with a d. Is that right?

Yes! In Dutch, any d at the very end of a word is pronounced like a 't'. It is spelled with a d because if you make it plural (honden), the letter moves to the middle of the word and sounds like a 'd' again.

Could I change the order and say Daar de hond slaapt?

Not quite. You can start the sentence with Daar to emphasize it, but Dutch uses a strict 'verb second' rule in normal sentences. If Daar takes the first position, the verb slaapt must immediately follow it in the second position. The correct order would be: Daar slaapt de hond.