Learn Farsi: چوب نم‌کشیده راحت نمی‌سوزد.

It perfectly demonstrates the pattern of combining a noun with a past participle to show a resulting state. نم means moisture, and کشیده is the past participle of کشیدن (to draw or pull). Together, they describe the wood's acquired state: 'having drawn moisture' or 'damp'.

Could I just use the simpler word خیس (wet) instead of نم‌کشیده?

You could be understood, but they have different nuances. خیس generally means actively wet or soaked. نم‌کشیده specifically highlights the state of a material having gradually absorbed ambient humidity or dampness over time, which makes it the most natural word for this context.

Why is راحت translated as 'easily' instead of 'comfortable'?

In Farsi, many adjectives can function directly as adverbs to modify verbs, without needing a special ending like '-ly' in English. Because راحت describes how the verb نمی‌سوزد happens, it means the wood does not burn 'easily' or 'without difficulty'.

Is the verb نمی‌سوزد transitive or intransitive in this sentence?

It is intransitive here, meaning the wood is doing the burning (or rather, not burning) itself. It comes from the infinitive سوختن (to burn). If you wanted to say someone is burning the wood (transitive), you would need the causative version of this verb, which is سوزاندن.