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:

A list with other manufacturers:

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: