The first is an ordered list which means that each item on the list is numbered, this would be used for like ordering steps. The second list is unordered lists which is just like bullet points. The last is definition terms which is a list of names with a definition below them.
The first group changes the font and appearance like what typeface is used and whether it is bold, italic or the size. The second group does not change the text but rather things like the color, spacing, and other decorative elements. The formation of the text can change how readable your webpage is.
Most browsers will only be able to display typefaces that are installed on the computer so if you choose one that is not installed it will not show on other computers. You can use other fonts that are not standard to computers, but you need to define these in the CSS. There are a few different ways to do this, some concerns would be that the font has copyright or that it may look different on a Mac or PC.