For buying a laptop it depends upon your purpose what for your are buying it.
If you are buying a laptop for everyday use for official task and assignment then the configuration should be
Brand: I highly recommend HP or DELL
Processor: Intel core i3 or higher
RAM: 4GB or hihger
HDD: 1TB 5400 rpm SATA or higher
Battery: 4 cell Li-ion
and NO need of graphics card for this purpose.
If you are buying a laptop for gaming movies or for codding then the configuration should be
Brand: I highly recommend HP or DELL
Processor: Intel core i5 or higher
Graphics: 2GB NVDIA or higher
RAM: 8GB or hihger
HDD: 2TB 7400 rpm SATA or higher
Battery: 6 cell Li-ion