Play around with -> http://oriondemo.solarwinds.com/
In general terms NPM is best suited for monitoring Device Up/Down, CPU, Memory, Disk and lastly interfaces (up/down, utilization, bandwidth etc), now when it comes to the interfaces NPM provides you with a high level overview on what's happening with on the interface, if you want to dig deep as to which host or which application or which conversation is consuming how much bytes/packets via that interface is when you would need NTA which does a deep dive and collects that information for you via netflow (which needs to be enabled on the end device for NTA to collect the information).
Login into SolarWinds demo -> My Dashboards -> Netflow -> NTA Summary (check this out, you would understand whats being done through NTA, that explains all)
and for NPM on demo -> My Dashboards -> Network -> NPM Summary
play around with the demo, its self explanatory....
Hope it helps
Thank you Vinay
Inventory, Status, Response Time, Utilized % -> NPM
% traffic per app/port/conversation, source/dest -> NTA