A digital library is a platform where you can find content such as books, audio books, videos and files electronically. In this type of library there is no physical infrastructure. Everything is done on the web.
It is usual that the institutions to which you belong (school, university, local library or company) already have a platform to offer this content, therefore, it is only necessary to register on the platform used by the institution.
Although digital libraries are not intended to replace physical libraries, in times of virtuality, such as the one we live in today, they can be of great help to users and library staff.
It also has some advantages, such as:
Better interaction with resources
Variety of formats
Here are some links to digital libraries: