HTML is all about the right use of tags.If u want to develop any web page,First u have an idea that how it looks like or what will be the apperance of the page,then just use the tags and here is your page.
Tags:
1. < b > tag: for boldness of fonts.Also we can use < strong > tag at the place of < b > tag.
2. < i > tag: for italic shape fonts.Also we can use < em > tag at the place of < i > tag.
3. < u >  tag: for underline the desired fonts.
4. < del >,< strike > tag : for deletion.
5. < big > tag : to increase the  font size.
6.  < small > tag : to decrease the font size.
7. < sup > tag : super script.
8. < sub > tag : sub script.
LETS HAVE A SIMPLE PROGRAM WITH ALL THESE TAGS:

< html >

< head >

< title > HTML tags < /title >

< /head >

< body >

< b > Bold text < /b >

< i > Italic text < /i >

< strong > Bold text < /strong >

< em > Italic text < /i >

< u > Underline text < /u >

< big > large size font < /big >

< small > small size font < /small >

X < sup > 2 < /sup >

H < sub > 2 < /sub > O

< /body >

< /html >

TRY IT..its intersting and make u more understandble to tags.
NOTE : When we use multiple tags ,just remeber close the tag first which you opens recently.
for example:

< body >

< b >< i > Hello ! have a nice day .< u > BY SHEAVY JATTANA. < /i>< /b >

< /body >

Note: No space is allowed inbetween the tags.

< i > ------right

<     i >------wrong.