Quick answer
В в is the v of “van”. The Russian letter for b is Б б — a different shape with a flat top.
v
How to say it
Say “van”. That is В. Before a voiceless consonant or at the end of a word it hardens to f: во́дка is “vodka”, but в ко́мнате sounds like “f komnate”.
В as a preposition
On its own, в is the preposition “in / into”. A single letter can be a whole word: в Москве́ (in Moscow), в шко́лу (to school). It merges into the next word in speech and is never stressed.
Не vs Ве
Learners reading quickly turn вода́ into “boda”. Fix it with the pair вода́ — борода́ (water — beard): the first is В, the second Б.
Typical mistakes
Reading Москва́ as “Moskba”
“Moskva”
В is always v.
Writing B for в in handwriting
В has two bellies, Б one with a flat lid
The shapes are genuinely different once you slow down.
Check yourself
Which word contains В?