Create a simple plugin

I need to create a simple booking widget plugin with from date, to date, no of adults and book now button. When we click on book now button, the plugin has to collect the selected values from from date , to date, and adults and then go to a new domain. the other domain is a completely different site. When the "Book now" button clicked we need to create a url with those values to fit to the other domain. You dont have to worry about booking. just have to generate a url This is a simple plugin. We need to create this as a plugin because we have to use it in different themes.