The recent progress in Information and Communication Technologies gave birth to advanced applications in the field of instrumental e-learning. However, most of these applications only propose a limited number of lessons on predetermined pieces, according to the vision of a single music expert. Thus, this article introduces a web platform to create music lessons dynamically and collaboratively, with the assistance of a semi-automatic score annotation module: @-MUSE. To do so, we first describe a new methodology to design such a platform: Sign Management. Then, we detail its general architecture as an Iterative Sign Base System based on a common practice in music learning: score annotation. Lastly, we give various algorithms to generate relevant annotations (explanations) on a score, based on the analysis of musical patterns difficulty.