Did you know there's a right way to say a number? Most of us understand just fine even if the speaker doesn't follow the rules, but the rules help.
1. The only time you say "and" is when you're identifying the location of the decimal point. 123.456 is read as "one hundred twenty-three AND four hundred fifty-six thousandths", and not "one hundred AND twenty-three", etc.
2. Every three numbers to the left of the decimal is a set of hundreds, just with a possible extra word. How do you say 123? "One hundred twenty-three". How do you say 123,000? "One hundred twenty-three ... thousand." What about 123,456,789? "One hundred twenty-three ... million, four hundred fifty-six ... thousand, seven hundred eighty-nine".
3. Long strings of decimal numbers can appear pretty daunting. For example, how do you say this number out loud? 12.34567809. First, you put in commas, counting from the right, every three places, just as you would with the numbers to the left of the decimal. It now looks like this: 12.34,567,809. Read it just like a "normal" number, but add "hundred-millionths" at the end. "Twelve and thirty-four million, five hundred sixty-seven thousand, eight hundred nine hundred-millionths".