Typography is the soul of design, it lies at the heart of visual literacy. In its essence, typography is a powerful medium that allows precise, effective communication. Typography is not only about choosing the best font family, but about bringing value to communication and making information better understood by the audience.

Beautiful typography & letters are everywhere. The creativity of offline lettering and type is just starting to be used online.
Until recently, using any typefaces, beyond those installed with computer operating systems (known as web-safe fonts), by default meant using images, Flash, or some other workaround. Browser makers made situation much better by implementing the @font-face CSS property, which allows designers to link to any font file and pull it into their pages.
But many typefaces were never meant for screen use, either because they’re aesthetically unsuitable or because they’re just plain illegible.
Being a web designer will require a deeper understanding of typography and how typefaces work.
The number of available typefaces in web design increases every day and since much of the web is made of text, web typography is a powerful tool.

Legibility

is affected by typeface design. We can’t change how established typefaces look, but we can select the right one and set it accordingly. Uppercase letters are considered more difficult to scan then lowercase letters, while regular type is more legible then italics. Good contrast between background and body copy, appropriate line lenght and line height increases legibility.
High x-heights and a strong character body help keep your texts legible, even at small sizes. For example, Verdana and Georgia, have a larger x-height and more space between the letters so that text keeps clarity even at small sizes.

Readability

it’s influenced by layout, the placement of block of content and the presentation of individual items. Reading a long passage in a blackletter face would take much more time than reading same passage in a basic serif face.
To ensure readability we need to consider:
- Line length is the lenght of individual lines of text. The optimal lenght will depend on context, but between 45 and 85 characters is recommended for comfortable reading and it doesn’t require eye to travel much from the end of one line to beginning of the next.
- Line height is the space between two consecutive lines of text. By default browsers set a line height of 1 x font size, which is too small to be legible. Widely accepted rule is to set line height to 1.5 x font size. Simple guide is – the longer the line lenght, the greater line height.
- Letter spacing is the space between letters. Pair of characters in certain serifed typefaces can sometimes overlap. When experimenting with letter spacing, make sure that “AV”, “ft” and “co” are clearly readable. Also check that “vv” and “w” are distinguishable. Smallest inaccuracy can make text completely unreadable.

Contrast

is important because not all the content within a page have the same value. Most online readers don’t read line by line, instead they scan from one point to another. By creating contrast you direct the reader’s attention to the important messages.
One of the easiest ways to quickly create balance and contrast in typography is to choose a serif and sans serif pairing.
When pairing typefaces, it’s important to be able to tell that there are two distinct typefaces. Similar typefaces can weaken the message.

Because web typography is all about communication with readers, make sure that conversation is rich and meaningful; readers will appreciate it. At the end I would like to quote Robert Bringhurst, author of typographic bible The Elements of Typographic Style:

Typography exists to honor content