crystal report parameters field help

Question

i am developing a windows application, I have my database in MS-Access. I want to create a crystal report which have the fields License key, Activation Date, Expiry date. I want to add parameters field in this report which will have activation date as Start date and Expiry date as End date. I have no knowledge of parameters field in crystal report. Please help me out with the coding and the steps how to add the start date and end date in the crystal report.