Is there somewhere or somehow a manual where I can learn how to record my bass , why to use preamps, how it works and stuff ??

nobody ?

This is an extremely wide topic:

You can start here:

http://www.recordingwebsite.com/

Read the FAQs here:

http://www.harmony-central.com/Recording/

http://www.bownie.com/guide/recording/

There's tons of links:

http://www.google.de/search?q=audio+recording+guide&hl=de&start=10&sa=N

www.homerecording.com is a good place too

http://www.audio-recording-center.com/article-bass-sounds.html