Can someone explain these 2 variable types to me please. integers & longs i understand but these 2 i'm not sure about.

I dim dbDub as Double and i set its value to 111,111,111,111,111 and it = 111billion,111million,111thousond,111. But when i add 1 more 1 it all of a sudden = 1.11111111111111E+15.

Now what does this mean? does it mean i now have 1.1 as a value or do i have 1 trillion,111billion,etc....

What is the difference in speed as compared to Longs and Integers?

Would i only use Doubles and Singles when i need to use decimal places?

Thanks!