Loading your kayak onto your car by yourself can be challenging, so it's good to have a reliable rack system. There are plenty to choose from and there are even some that will lift your kayak up onto your roof for you.
If you have factory racks already on your vehicle, you can buy rack accessories specific to kayaks to fit them. But if your vehicle doesn't have factory racks, then you'll need to invest in basic towers to support the accessories. Basic towers are usually stronger and support more weight than factory racks, so you may want to go ahead and invest in the towers regardless.
A common type of kayak rack are J-shaped cradles that hold your boat in place and make it easy to tie the kayak down. Cam straps make tying boats down very simple. It's best to throw the cams through the J-cradles first, load your boat, and then tie the boat down. Thread the end of the cam through the metal buckle and pull down. You'll want to position the buckle of the cam so that you can pull down to tighten the strap. The end of the cam without the buckle will wrap around the bottom edge of the cradle.
With the cradles, you'll have to lift the boat over your head to put the kayak in place. To do this, place, one hand on the front of the cockpit and the other on the back of the cockpit. Bend your knees and lift the kayak up to thigh level. Bend one knee to support the boat. From here, you'll want to lift the kayak over your head and place it on the cradles.
If lifting your kayak over your head is too strenuous, you can ask a friend to help by taking one end of the kayak at the grab loop while you take the other end. This way you can both lift together.
You'll want to make sure that your kayak is firmly secured to the top of your vehicle by using a bow and stern line from the kayak to the bumpers of the vehicle. You can use regular ropes or cam straps or get specialized bow and stern tie-downs. The bow and stern lines ensure that the wind can't pick up your kayak and rip it off the racks.
If you're going to be loading your boat mostly by yourself, then you'll want to look at getting a lighter boat or investing in a more expensive rack system that will help lift your boat for you.