GnuGo is good enough to get started but you should not play many games with it. Just a handful to get acquainted with the rules. Playing against computers will

GnuGo is good enough to get started but you should not play many games with it. Just a handful to get acquainted with the rules. Playing against computers will teach you bad habits and will not be helpful past the very basics. If you want to do exercises, try e.g. Tsumego (for Android at least). And the best way to get started is to find your local Go club, take a friend with similar level to you (ie. complete novice) and join their game night (my local go clubs meet in bars). Ask a more experienced player to over-the-shoulder for a few games. This is how I got started.