Radagast is a member of Gandalf's order, a Wizard who lives at Rhosgobel, near the borders of Mirkwood. He is not a great traveler, but he is excellent at taming birds and animals to carry messages and help him when he needs them. Radagast meets Gandalf at the end of June of the year Frodo leaves the Shire. He carries a message that the Nine Nazgûl are abroad.
Following this development, Radagast tells Gandalf that Saruman the White now wants to speak to him about helping Gandalf in his quest for the Ring. Thanks to Radagast's message, Gandalf travels immediately to see Saruman – leading to the horrible delay that almost prevents Frodo from leaving the Shire.
Radagast is taken in by Saruman's deceptions and manages to help Saruman trick Gandalf as a result. But he makes up for his mistake: Radagast speaks to his bird friends to gather information about the Ring. He sends them to Gandalf to relay their news. As a result, Gwaihir the Windlord, the fastest of the Great Eagles, comes to speak to Gandalf at the top of Orthanc.