I'm new user in turtelbot 2;

I have some questions

1- when we use the netbook (basic configurating), it's necessary to connect the netbook with turtelbot2 via usb cable? 2- when we will test some package like RGBDSLAM, it's preinstalled or we must to download in the netbook. 3- when we verify the connection from Turtelbot to ROS master, we get the following error " Unable to communicate with master", then we use ssh, but it still the same error.

Finally, please if you have some videos or tutorials for how to start the turtlbot, can send it.

thanks for your helps.