It is not to hard to master this method of growing potatoes. One problem with these bags is that they do not drain water well which will require you to add some holes so water drains properly. This will actually be the fun part of the process.
You want to use a mixture of potting soil and compost in the bag. The more nutrients you provide for the potatoes the better the crop you will grow. Only partially fill the bag, so it is not to heavy to handle. The video below will walk you through all the steps to prepare the bag, plus plant and care for your potatoes.