Learn Finnish: Matto pöydän alla tuntuu karkealta. - The rug under the table feels rough.

This is because of the verb tuntua (to feel). In Finnish, perception verbs like tuntua, näyttää (to look), and kuulostaa (to sound) require the descriptive word to be in the ablative case, which adds -lta or -ltä. You are essentially saying that the rug gives off a feeling "from rough".

Why is the word for table written as pöydän instead of pöytä?

The word alla (under) is a postposition. Most postpositions in Finnish require the noun directly in front of them to be in the genitive case, which adds an -n to the end.

Why did the letter t in pöytä change to a d in pöydän?

This happens because of consonant gradation. When you add the genitive ending -n, it closes the final syllable of pöytä. This forces the strong consonant t to soften into the weak consonant d.

Can I use tuntuu to say that I personally feel happy or cold?