Generally, use tax applies when a person or business in California purchases tangible merchandise to be used, consumed, given away, or stored in California from a retailer who does not collect California tax on the sale. In other words, if sales tax would apply when a particular item is purchased in California, use tax applies when a similar purchase is made from a retailer outside the state and tax is not charged.More information about this use tax can be obtained at:

http://www.boe.ca.gov/sutax/useTaxRegFAQ.htm#usetax2