The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. 

Data/Information generally stored in any HLR:- 
    1. MSISDN and IMSI number of each subscriber.
    2. Authentication information.
    3. GSM services that the subscriber has been provisioned with. 
    4. EDGE / GPRS parameters to allow the subscriber to access packet services. 
    5. Current location of subscriber (VLR and SGSN). 
    6. Supplementary service (call waiting) settings applicable for each subscriber. 

Main functions of HLR:- 
    1. Subscriber data management. 
    2. Store and provide subscriber authentication information to MSC and SGSN. 
    3. Manage the mobility of any subscribers by means of updating their VLR,SGSN address.
    4. Send or remove subscriber data in  VLR or SGSN as new subscriber enters or exits.
    5. Communicate with MSC/GMSC during call set up.
    6. USSD call routing 

though basic things but properly written

important for beginners 

good basic writing 

useful document, thanks