Mechanisms of electron phase separation in manganite-type oxide materials are analyzed using a simple Kondo-lattice model with intersite Coulomb repulsion between electrons. This model predicts the instability of magnetic (or charge) homogeneous ordering toward the formation of droplet structures (magnetic polarons) for a wide parameter range in the phase diagram. Various types of magnetic polarons are examined. The transport properties and noise spectrum of phase-separated materials are also discussed.