The chemical synthesizer is one of the machines added by MineChem. The chemical synthesizer is used to create new compounds or items from elements and other compounds. It requires power supplied either from Universal Electricity (Minecraft 1.6.4 or older), or Thermal Exapnsion (Minecraft 1.7.2 or newer) unless otherwise disabled in the config file. 

When properly powered, it can be used to create new compounds/items with appropriate recipes. These are for you to find out, or to read elsewhere on the wiki.