changing language and background color and size

need help i'm new here MY WEB ARE FOR A FRENCH AUDIENCE(USERS) HOW TO CHANGE THE LANGUAGE (TO FRENCH)AS I COULDN'T FIND ANYTHING IN THE ADMIN PANEL.
I WOULD LIKE TO CHANGE THE BACKGROUND AS WELL AS THE SIZE OF THE SCRIPT MAKE IT A BIT WIDER.
WERE TO GO,I DON'T KNOW WERE TO LOCATE THE CHANNEL FILE OR WERE TO FIND THE HTML CODE FOR ANY MODIFICATION SORRY BUT I'M NOT GOOD IN IT

You have to edit template files, for site width edit header.tpl and for language change i think you should edit
all tpl files.