There isn't a huge difference in adding the grape pack, truthfully. The most challenging part is getting the grapes out of the plastic and into the mesh bag. The best way I've found to deal with that is to put the bag in a bowl, secured to the rim. Then you can more easily pour the skins out of the plastic and into the bag. When you're done, tie a knot in the bag and you're off to the races. Oh, and if your kit calls for oak powder or chips in primary, put those in the bag too. It makes that first racking SO much easier.
Be aware that the sugars in the grape pack may take a bit to dissolve and as a result, your initial SG reading might be low. I've gotten into the habit of mixing up the kit, adding the grape pack, then stirring a few times over the next several hours before pitching the yeast. As an example, I started an Eclipse Merlot kit on Sunday. When I first mixed up the juice, SG was 1.080. After adding the grape pack and stirring, it was 1.094. Four hours later, after another stirring or two, SG was 1.100. The following morning, a cap had formed and I clearly had fermentation going on, but SG was still at 1.100. I estimate my SG peaked at 1.102 on this one.