first type your text, then select it, (so it looks blue with white letters) then choose the font, size and color you want. Your text will after that look like this:
[ FONT=Arial]text text text[/font] this is for changing font
[ SIZE=7]text text text [/size] [SIZE=14pt]this is for size[/SIZE]
[ COLOR=red]text text text[/color] this is for color
[SIZE=14pt]and all together:[/SIZE] [ FONT=Arial][ SIZE=7][ COLOR=red]text[/color][/size][/font]
you have to make sure that you also put all the [/color][/size][/font] at the end, otherwise it wont work.