Every 3D printer has a buildplate/printbed, where the 3D print will be build upon. This can be made from different materials, like glass, kapton, PEI, aluminum and painters tape. Trick is to have the 3D print adhere to the bed during printing, as obviously the print would fail when it comes loose, but the print should be easily removed from the bed after printing.
By heating your printbed, making it a heated bed, the 3D print will stick better to the surface. While cooling down, the plastic will shrink a bit, making it come off more easily. By heating the printbed, the plastic shrinks also less during printing, fixing it better to the bed and reduce the warping effect (where the corners of the print come loose from the bed).
Some common temperatures for a heated bed, with 3Dlac include: