Questions & Answers about Вечером я хочу просто расслабиться.
In Russian, time expressions like утром (in the morning), днём (in the daytime), вечером (in the evening), ночью (at night) use a special case form (historically instrumental) without a preposition to mean “at that time of day.”
So:
- вечер = evening (basic dictionary form)
- вечером = (in) the evening / this evening (adverbial use)
You do not say в вечер in this meaning. Common options are:
- вечером – in the evening / this evening
- сегодня вечером – this evening (more explicit)
- по вечерам – in the evenings / in the evenings generally (habitually)
На вечер exists, but it means something different, like “for the evening” in scheduling, e.g. планы на вечер – plans for the evening.