The dual-core processor should be sufficient in a laptop for normal user. The primary function of the cores is to allow the computer to multitask. Hence, you can run several applications at the same time.
A quad-core CPU will be better if you are a heavy user.
Otherwise, if you are into jobs like photo editing, music production, or working on other complicated engineering software, you should choose a laptop with hexa-core or octa-core processor.