i3wm how to configure for xterm

Hi I just installed the i3 Window Manager. First of all, it is a graet wm for me.
So I want to autostart 3 Workspaces when i3 starts:
No.1: 2x Xterm: horizontal
No.2: 1x Xterm: Screen on, runnining irssi and some IM
No.3: Firefox

I think i have to change the i3/conf but don't know were i have to set it up.

I found some source on the web here. But it isn´t so helpful for me.
man i3

Straight from the man page,
 When starting, i3 looks for configuration files in the following order:

        1. ~/.config/i3/config (or $XDG_CONFIG_HOME/i3/config if set)

        2. /etc/xdg/i3/config (or $XDG_CONFIG_DIRS/i3/config if set)

        3. ~/.i3/config

        4. /etc/i3/config

       You can specify a custom path using the -c option.

If you're simply looking for the sample config file then I suggest looking in /usr/local/etc/i3