The easiest way to start is to buy a laptop/computer that already has Ubuntu installed on it

Dell ist probably the most established and well known manufacturer who delivers laptops/computers with pre-installed Ubuntu to selected regions:
http://www.dell.com

A list with other manufacturers:
https://help.ubuntu.com/community/UbuntuPre-installed

If you don't buy a laptops/computer with an Ubuntu pre-configuration, choose a "Ubuntu certified" model from Dell, Wipro, HP, Lenovo, ASUS, Acer, HCL Infosystems Limited or Toshiba:
http://www.ubuntu.com/certification/desktop/

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