Engine shafts are supported by bearings. Some of them can handle axial and radial loads. Other bearings are cylindrical roller bearings only used for radial loads. The bearings have to be in bearing sumps, which is part of the oil system, and the oil has to be kept within the system by the shaft in the different oil sumps. Engines typically have 2 and 3 shafts: HP, LP and IP shafts. The rotating parts (shafts and discs) are supported by bearings in oil sumps for proper lubrication.
Various types of seals provide the sealing of oil areas; these are usually labyrinth seals, but Carbon (nickel graphite) seals may also be used in some places.