Have you checked out the github readme's? I still have to do the one for bitshares checkout but the plugin instructions are all done already in each of the readme's
Installing them is straightforward, 1 to 5 steps. Takes 10 mins max. If you have to install the cart system maybe 30 mins tops.
Essentially you just copy the files to your root folder of your cart installation, and then go into the cart admin and add the payment gateway or enable..
Configuration happens in config.php which is usually just setting up salt's and RPC settings.