Yes it is very easy.
Cut the rind with the fat on into pieces about 1''square, drop them all in a empty deep frypan, put on low, the fat will begin to melt as it does leave a little bit in the pan but drain most of it off. keep going until practically no fat comes out. The pieces will shrink and darken a bit, You must keep the heat low or they will get too dark, It takes a while and best to keep an eye on it. You can if you wish do it in the oven in the same way but you are lifting the pan in and out, do whichever is most comfortable for you. When the fat is much less you can press on the bits to extrude even more. While they are still warm, salt them too your liking and that;s basically it...cracklings..or as the English call pork scratchings
All you are doing it removing most of the fat and in doing so the skin gets crunchy.
I like to get a piece of pork with the fat still on, then I slice through the rind every 1/4 inch or so across one side,don't cross hatch, then roast the pork as usual. the crackling cooks on top of the pork in long thin strips, it is a bit different to the pan done scratchings as the skin blisters in the heat of the oven.
Oh and don't throw the fat away that you get, it is of course pure lard and is wonderful to roast potatoes in. Oh and by the way I do make these quite regularly.
I have just re read your post and you mention the ones that come in the bag, there are two types, if you are talking about little bags and the rinds are hard this is similar to what is above, if you are talking about the ones that look like puffs and come in big bags, you can't make those at home I don't think as they are air blown I believe.
There is a way to extract the fat using water but that is more to get the fat than the scratchings.
Enjoy