How do you take out an injunction?

This depends upon your state's laws and to some degree its court rules. You get an injunction by filing with the appropriate court a complaint or petition alleging the reasons you are entitled to the injunction. The papers are served on the defendant and ultimately there will be a trial in the usual way. If the court agrees with you, it will issue an injunction to prohibit the other party from doing whatever it was doing that was wrong.