Integrated DNA Technologies sells short strands of DNA called oligonucleotides. In order to better understand how these are useful, you'll have to know a bit about DNA itself.
DNA is "the blueprint for life" and encodes instructions for all of life's processes. DNA is a complex long thin molecule (strand) that is made from 4 possible building blocks called "bases". These bases are called Adenine, Cytosine, Guanine and Thymine, and the precise order of these bases is a code for information. In living organisms, DNA strands can be millions of bases long and therefore contain huge amounts of information. This complexity is responsible for the vast complexity and diversity of life on earth.
The way that one strand of DNA specifically binds a second strand of DNA allows scientists to use short DNA strands (oligos) as research tools. A short synthetic piece of DNA (usually around 20 bases long) can be used to bind or find its matching sequence even in a complex mixture of millions of unrelated pieces of DNA. It is this unique fact that allows researchers to decode and study the genetic makeup of any living organism.
Using new oligo-based technologies, a revolution is underway where they are beginning to catalog the complete genetic makeup of hundreds of living things, ranging from bacteria to humans. The human genome alone contains over 3 billion bases of DNA, so projects of this kind tend to be very complex and often take years to complete.
Scientists often start the research knowing the DNA sequence for the organism that they are interested in studying. Given a known DNA sequence, they can easily design a short oligo that can be used to perform a variety of tasks. It is this short single-stranded DNA that the researcher orders from IDT. Living systems don't discriminate DNA that is synthesized chemically from DNA taken directly from an organism, allowing researchers to use IDT's custom made oligonucleotides as if they had existed naturally.
IDT manufactures the oligo using chemical DNA synthesis machines designed and built in-house. They've refined the process to the point where they can receive an order as late as 1:00pm and have the desired oligo in the researcher's hands the next morning. Their customers range from small university labs of only a few scientists to global pharmaceutical companies, and everything in between.