Your several questions/answers depend on the engine.
Some engines use a seal on the camshaft end to retain lube. Most american OHV V-8 that we deal with have a soft plug installed to retain lube. Cams can be removed from the rear on many engines. One example a few people on here can remember is the Chevette or the Pinto.
Some camshafts are open to the front/rear of an engine to drive various accessories. Distrib, pumps etc.