FOSS gamedev and creative worlds

Hi everyone!
Lets say I wanted to suggest new mobs or something, how do you make/what program do you use to make the graphics and is there a scripting/coding tutorial here?
Thanks ^^

GIMP, Mtpaint, Mypaint…

thanks :D
btw can i also use photoshop, paint, or graphicsgale?

Also, how else can I help? I dont really know what programming language the game is in.(I am familiar with visual basic though)