For non-realtime (including non-linear, like montage) processing you need only plugins
(ladspa, lv2, vamp) and some editor like Audacity, mhWaveEdit or something other.
For realtime (also called non-destructive editing... hm, probably, they are right :) you
need set of various software, that could be used at one time and be connected each to
other).
It would be better for you to begin with special distros, where all necessary staff is
installed and has good settings out of box. My favorite is kxstudio, as (imho), best
variant vor newbies.
Lookup for some (or more) articles and videos.