To talk to a Furby, make sure you are directly facing him/her and speak slowly and clearly. The closer you are to the Furby, the easier it is for him/her to hear and understand you. Furby toys are easily distracted, so you should keep background noise to a minimum.
If your Furby is not responding to your voice or is acting "strange," then first check to see if the batteries need replacing. Furby toys have also been occasionally known to fall "deeply" asleep, and you may have trouble waking up your toy. Simply remove the base, press the reset button for 2 seconds, and then replace the base. Doing this resets the hardware while retaining all the personality data, so you won't have to worry about retraining your Furby.
All Furbys initially have the same personality. Your Furby's personality develops according to how you speak to and play with him/her. According to Hasbro, some of the personalities your Furby may develop include Rockin, Sweet, Hyper, Jolly, and/or Fiesty.
In addition, your Furby may also enjoy talking to and spending time with other Furbys depending on his/her personality. To have your Furby communicate with others, make sure the Furbys are no more than 3 to 5 inches apart and that background noise is at a minimum.