Chucker: strong.presenter {} would be if he was assigning the class to the strong tag itself.
Torifile: # is for an ID, . is for a class. IDs are only usable once in the page, which is handy for debugging - most developers use them for block level elements that are significant structures on the page (wrapper DIVs, navigation DIVs and so on and so forth). A class can be applied to anything but is generally the weapon of choice for an inline element because you are more likely to use something like a span or paragraph more than once.
If you have element.className then the class applies only to elements bearing that class.
If you have .className then you can apply that class to any element.
If you have .className element then the cascade applies the properties of the class to every element within that class - so:
.redText p {text-decoration:underline}
would make every paragraph within .redText underlined.
The same applies for IDs, just replace the full-stops with hashes.
HTH. Any other questions, just ask - there aren't many things I can be of much help with, but this is one of them
Edit: strong and em are two completely different things to b and i. But that's a different can-of-worms for a different day