Learn Russian: Вечер тихий, и беседа течёт плавно. - The evening is quiet, and the conversation flows smoothly.

Течь literally means "to flow" (like a river). Metaphorically, it acts as a unidirectional Verb of Motion describing things that proceed continuously in one direction, like time or a беседа (conversation). Unlike core motion verbs (like идти or ходить), течь doesn't have a direct multidirectional equivalent used in everyday speech, making it simpler to use when describing an ongoing, forward-moving process.

What is the difference between беседа and the more common word разговор?

Разговор is the most general word for a talk or conversation. Беседа, on the other hand, implies a more prolonged, pleasant, and meaningful discussion, often in a relaxed setting. It perfectly matches the calm, atmospheric mood of a quiet evening flowing smoothly.

Why use the long-form adjective тихий here instead of the short-form тих, since it means "The evening is quiet"?

While short-form adjectives (like тих) are often used as predicates to show a temporary state, the long form тихий is perfectly fine here and gives the sentence a more descriptive, atmospheric feel. It paints a picture of the inherent quality of the evening, rather than just stating a bare, temporary fact.

Could I use the adverb гладко instead of плавно for "smoothly"?