Mariusz - have a look at
strobist and the associated
strobist flickr group...
Particularly on Strobist, there's a section called 'Lighting 101 archive', which is one of the drop-down manue about halfway down the page (under the flash ads). This is one of Strobist's key learning tools; although it relates to off-camera flash on the whole, the ideas it teaches are simple to follow and David Hobby's writing style is really easy to understand.
On the strobist flickr group there are some good threads in the discussion area, and a search should yield something if it's not immediately visible. There are a fair few bolshy, elitist people (mainly americans) on there that don't appreciate that some people are new to it all, but post a sensible thread and you'll get sensible answers
The strobist stuff would probably help you more with the outdoor portraiture, although if you really want to harness that learning then some kind of off-camera triggering (cables/wireless triggers) is probably going to help you out in the long run.
As for night club stuff, most people go for slow sync flash to expose the subject with the flash (in turn, getting it sharp) but letting the camera use a slow shutter speed to '
burn in' the club lights to give you a real contrast in light colour and some background movement. This is all about exposing the subject using the flash (to render then sharp and evenly exposed) but leaving the shutter open for a long time to let the ambient light build up to a level where it adds to the image. Here's a good tutorial about it:
http://strobist.blogspot.com/2007/09/lighting-102-33-balancing-flashambient.html
This is something I rarely do in my line of work, so I'm not best placed to give you a full rundown of how to do this, but it's worth searching on the web for "
slow sync flash" and "
rear curtain flash", two key phrases that relate to nightclub photography....
There are also some tutorials on TP that might help...
http://www.talkphotography.co.uk/forums/showthread.php?t=10271
http://www.talkphotography.co.uk/forums/showthread.php?t=225514
http://www.talkphotography.co.uk/forums/showthread.php?t=303374
...and others on the web that cover things you want to know:
http://www.digital-photography-school.com/slow-sync-flash
http://www.digital-photography-scho...-of-2nd-curtain-sync-flash-or-slow-sync-flash
