Each subdirectory should be a separated version of Share. Someone told me to use one sandbox per each instance. Where I can find the docs to understand how to proceed?
For this you need the multi-tenant capabilities of Alfresco - the ability to have multiple repositories hosted within a single server instance, i.e. multiple Company Home roots and multiple indexes.
However, the Share application does not yet fully support multi-tenant - it is being fixed up fully for 3.2.