Roundup Ready sugar beets H7-1 was developed by first making a piece of DNA, called an expression cassette, that contains the cp4 epsps gene for tolerance to the herbicide glyphosate, which is the active ingredient in Roundup agricultural herbicides. Using genetic-engineering techniques, that expression cassette is spliced into a plasmid and transformed into Agrobacterium. The Agrobacterium is then added to a petri dish containing sugar beet cells growing in tissue culture. The Agrobacterium uses a natural process to insert that expression cassette into the genome of the plant. The DNA of the resulting plant then contains the cp4 epsps gene and has a tolerance to glyphosate. The process is not unique to sugar beets and is used to develop most GM plants. A detailed description of the process is available in the USDA petition, starting on page 19: http://www.aphis.usda.gov/brs/aphisdocs/03_32301p.pdf
There are also several YouTube videos that show the basic process for making GM plants using the Agrobacterium method.