Can anybody explain relations and formulas between mining share difficulty, target and hashrate?
Difficulty is a measure of how difficult it is to find a hash below a given target.
Target is a 256-bit number (extremely large) that all Bitcoin clients share. The SHA-256 hash of a block's header must be lower than or equal to the current target for the block to be accepted by the network.
Target = current difficulty = output by Bitcoin's getDifficulty RPC call (Difficulty is basically a different representation of the target to make it easier for normal humans to understand it.)
Hashrate is computed hashes per second.
difficulty = hashrate / (2^256 / max_target / intended_time_per_block) = hashrate / (2^256 / (2^208*65535) / 600) = hashrate / (2^48 / 65535 / 600) = hashrate / 7158388.055