Hello Gaby,

If you have a questionnaire and want to assess the contribution of each item to the final outcome, Cronbach's alpha simply provides you with an overall reliability coefficient for all variables or questions. If your questionnaire reflect different underlying qualities or dimensions, Cronbach's alpha will not be able to distinguish between these. In order to do further progress and then check their reliability by using Cronbach's alpha, you will initially need to perform tests such as principal components analysis (PCA). This is the basic concept in refinement of any questionnaire-based model, I hope it gives you some insights.