How can i send webrequest in background.js

my extension runns in background.js.
it reads the websiteresults and do anything based on the content from the result.
it save something in it make an popup and so on.

now i would like to made a webrequest automaticly in background

means i would like to call a website
and i must send headers like cooky and sending browser and this json as body {name: myname; doit:writing and so on}

how can i do that … i do not found anything for that … mybe my search are wrong.

thanks for any ideas …