adding attribute?!?!

Hello,

i´m a newbee... i´m a german and i try to write my best english...

ok 2my question

how can i put a new attribute(JavaScript events) to the Image or link...
by example...
i want to create this
onclick="myFunction('var');"
or onmouseover.... or mouse what ever...

<img height="291" width="346" src="/img/home.gif" alt="description Image"  onclick="myFunction('var');" />

and i mean not adding via QuellCode, i would change per dialogBox Link or Image

thanks 4 request

greets
Sven