Plumbing Course or Apprenticeship - if you can find one. Books are good - if you can find one. The internet is full of help and advice - some of it accurate. YouTube may have some videos.
If you have a specific problem you really need to say what it is - describe it - what is wrong with what.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix plumbing.