When hiking, how do I carry a tent and a sleeping bag?

You have 2 options, to put it in your backpack or outside of your pack.

If you have room in your backpack, just shove them in there, I'm not joking at all. It's better to put them in your backpack because its closer to your body, more firm, and closer to your center of mass. Depending on what kind of backpacking backpack you have, I'd recommend the following:

Internal Frame Backpack ( most popular you see at REI )
Put your sleeping bag inside the bottom of thisChina Pagoda Tents Suppliers bag. Just shove it in there, as small as it goes. Sleeping bags are bulky and don't need to be pulled out except when you're done hiking, so just get them out of the way. Usually you can buy compression straps at the stores to make them really really small.

Put your tent fabric ( fly, tarp, tent ) inside your pack as well.

Strap your tent poles to the outside, either vertically near the water containers or horizontally at the top or bottom of the pack.
External Frame Backpack ( these are the old school packs )
Put your sleeping back and tent in one giant stuff sack -- neatly rolled of course -- and strap it to the bottom section of the backpack. Make sure its tight!