basic questions – how to please

Hi,

I tried to google these answers but it might be easier just to ask someone
(just too much, – related topic to sift through)

I Would like to know how to upload to my site clean installs of software
if I wanted to start my website over.

Also, how & where do you insert the ‘shortcode’? or the other stringed code that has <?> – Is this how you change the theme & how do you know where to put it?

Thanks