The first will be underlined links, it's their text-decoration which is making the rules of said links the underlined text-decoration that rule is;

Code:

{text-decoration:underlined;}

if you want every link to not be underlined first find that rule (which are underlined) & delete every single effect to the rule "]{text-decoration:]underlined;}" & just input this;

Code:

a { text-decoration:none;}

(you only need to input this ONCE to take effect, not repetitively! Only if there is a different type of rule to it!

Now the second will be understanding rules. EVERY part to CSS which will actually make it work & to take effect are correctly written rules!
A simple rule would be like so;

Code:

a { text-decoration:none;}

the "a" rule is mostly common for links, many other sites may have different common rules depending on their CSS. CSS rule types must ALWAYS start & end with:

Code:

{

Code:

}

or else the CSS will mess up and become useless!
Opening & closing the parenthesis's are as common as opening and closing a door, it's how it works!

Understanding different rules for browsers & each pixel radius:
lets start off shall we with a quick border radius effect;

Code:

border-radius: 5px 5px 5px 5px;
-moz-border-radius: 5px 5px 5px 5px;
-webkit-border-radius: 5px 5px 5px 5px;

these are all 3 for browsers you all know & love.

Code:

border-radius: 5px 5px 5px 5px; - IE 7-9 (Internet Explorer), & Later browsers
-moz-border-radius: 5px 5px 5px 5px; - Mozilla Firefox, Maxathon & more
-webkit-border-radius: 5px 5px 5px 5px; - Google Chrome, Safari, Maxathon & more

Thanks a lot for providing such great tips, these are quite useful to me! Keep sharing more tricks and tips in future also.

Thanks !