Can someone explain to me exchange rates ?

$10 U.S. is not $10 Canadian.  If you are sending $10 to someone in Canada, the bank will need to convert the $10 U.S. to what it's worth in Canada.  It's currently worth $12.62 Canadian, so the bank will convert it and give you $12.62 Canadian.  However, there are charges for converting money, and a bank will not give you your best rate.

Every currency has different  value against other currencies.  

I'll use one I'm very familiar with. 1 US dollar is worth 48.58 Philippine pesos. So when I visit the Philippines and convert $100  US dollars to pesos I receive 4858 pesos. Then when I go to McDonald's for lunch where my quarter pounder value meal costs 185 pesos . 

  But the tourist from Germany will get even more pesos per Euro than I get per dollar while the Canadian will get less per Canadian dollar than I get for US dollar.

But remember places that actually change money give less than the official  exchange rate (its how they make money) so if I'm getting 48.58 pesos per dollar the official  exchange rate is probably 48.85..Worst rates are currency exchanges inside airports