Quick answer
Вы говори́те по-ру́сски. and Вы говори́те по-ру́сски? are the same words. Only the pitch tells them apart.
The yes-no question
Russian puts a sharp rise on the word being questioned, then drops. The rise is higher and steeper than in English, and it lands on whichever word matters: Вы говори́те по-ру́сски? (do you?) versus Вы говори́те по-ру́сски? with the rise on по-ру́сски (is that the language?).
Statements fall
A Russian statement falls further at the end than an English one. Keeping the pitch flat or slightly rising makes you sound uncertain or, worse, uninterested. The single most effective pronunciation fix for many learners is simply to let the voice drop properly at a full stop.
Why flat Russian sounds rude
Russian carries much of its politeness in the melody rather than in extra words. A request said flatly — Да́йте счёт — can sound like an order; the same words with a gentle rise on да́йте and a soft fall are perfectly friendly. This is why Russians often seem abrupt in English and learners often seem abrupt in Russian: both are using the wrong tune, not the wrong words.
Copy whole sentences
Intonation cannot be learned from a description. Take one recorded sentence, play it three times, and say it over the top of the recording until the shape matches. Ten sentences treated that way will do more than any amount of reading about pitch.
Typical mistakes
Adding a helper to form a question
Same words, rising pitch
Russian has no auxiliary for questions.
Flat, level delivery
Clear fall at the end of statements
A flat tune reads as disengaged or curt.
Check yourself
How does Russian turn a statement into a yes-no question?