Yes, kvraudio is the place to go for free VST and other plugins. VST is simply a plugin standard designed by Steinberg. There are other plugin versions - DXi by Cakewalk, RTAS by Protools, AU for Macs etc. In today's DAW, VST and DX are basically "native" - Cubase, Sonar, Ableton, Logic etc all reads them. All except RTAS which is Protools specific.
Plugins comes in various forms. They can be instruments (ie softsynths - or software synthesizers), samplers (ie softsamplers), or mastering/production etc (ie your reverb, effects, de-esser, compressor/limiter, equalizer etc).
And not all plugins are good, particularly free ones. In fact, many are mediocre. Some will crash your DAW, some will take up lots of CPU and RAM resources, some has poor quality. So try out the free ones at your own risks. Remember, your DAW should be as clean as possible. I don't like leaving useless plugins installed. In fact, installing anything may leave registry changes even after you uninstall it. So I would install with care - only those I'm sure I really want to try out and that has potential. So make sure you read reviews of free plugins carefully before even trying them out.
You mentioned "creating synth tracks". I'm not sure if you meant giving you synth sounds, or actually creating the tracks itself. For creating tracks, the one element that does it is... "human". There are loops etc that helps out a person who wants to do things the short-cut way, but in the end, the human factor is key. You cannot generate something (tracks) out of nothing.
