You don't have to have UV filters BUT they do protect the lens should you ever drop it.
DO NOT leave a CPL on the lens unless you are using it. The reason is that a Circular polarizing filter reduces the incomming light by at least 1 stop. It should only be fitted and used when you need the filter, for example to cut reflections off water, glass or to increase the blueness of the sky. A good general filter to have on a camera lens is a Skylight 1A or UV(0).
Please note: many professionals do not use UV or Skylight filters on lenses unless needed.
Have you used the search function? Your question is one that most newbies come across, hence it's often discussed. Secondly, reading up the basics of photographic filters will also help. CPL are not 'always on' filters. Whoever told you so is purposely misleading you.
for lens protection alone u can consider uv or maybe neutral lens as digital sensor is not that sensitive to uv rays compared to film. cpl is specific filter not a "walkabout" filter for lens as previous post mentioned