help me assign permissions to sharepoint online document library

Hi, I have an office 365 tenant with Sharepoint online for 10 users. The main document library has 10 folders. I would like to setup permissions so everyone will be able to read all documents of a specific folder. All other folders must be available for specific users. That is, only each user should be able to access a specific folder only. Please show me using [login to view URL] how to assign these permissions. Everyone will be able to read all documents should be implemented using an Azure AD security group. This should be a very easy job for the right person. Thanks