Can I open a certain website with a command line?

Have a look at xdg-open which uses the default program for opening the link:

xdg-open http://example.com

some documentation from Ubuntu:

xdg-open - opens a file or URL in the user’s preferred application

Use the command

firefox http://www.youtube.com

This should do it. 8 )

If you only need to open it in the background use:

wget http://askubuntu.com

To download a page (optionally mirror sub pages):

wget --mirror -p --convert-links -P ~/Desktop/ http://askubuntu.com/users/182026/kamil

If you want to open it and see it

and you use firefox:

firefox http://askubuntu.com

or you use google chrome

google-chrome http://askubuntu.com