You didn't say what kind of fishing you are doing. If you are attempting to fly fish, I can understand your problem. It is not easy to cast the line rather than the lure without some instruction. Many people try to cast the lure as if they were using a regular reel. In fly fishing, it is the line that is cast rather than the lure. The reel is just some place to store the line. One way to learn to cast the line is to forst take the tip end of a fly rod and attach a length of yarn to it. The yarn should be about 3 or 4 feet long. Take this rig out into your yard and cast the yarn so that it falls in a nice easy straight line in front of you. As you draw back for the back cast, look back and see that the line streaches out behind you before you start the forward cast. Yarn is light and will be easy to learn with. As you get better at casting the yarn, gradually lengthen it until you can cast a piece that is about 8 or 10 feet long. By this time you will have gotten the feel of casting line rather than casting the lure on the end of it. Now go put a "weight forward" line on your fly rod, reel out about 8 or 10 feet and start casting it just as you did with the yarn. As you improve, gradually lengthen the line until you can cast about 15 or so feet of line. Next, attach a fly that has no hook onto the end of the fly line and practice casting it. When you can cast the "blank" fly and make it go where you want, you are ready to go fly fishing.
O.K., that covers fly fishing but you may need to find some place that teaches fly fishing for sonme additional instruction to get your technique correct. Now on to spin casting. We will leave bait casting (traditional horizontal reel) for last. There are two types of spin casting reels. First there is the open face spinning reel and secondly there is the closed face spinning reel. Both have the reel aligned with the axis of the rod as opposed to the bait casting reel which has the reel at a right angle to the axis of the rod. Just as the names imply, the open face reel has no cover over the spool of line whereas the closed face has a cover that encloses the spool. Of the two, the closed face reel is the easier to learn to cast. It has a button on the rear that is depressed with the thumb to act as a brake on the line. To cast it, you simply first press the button and hold it, start your back cast by bringing the rod back over your head to a position slightly behind your ear. With a snap, bring it forward releasing your thumb on the break button just as your rod reaches a position of about 45 deg forward of your head. You may need to adjust this release point to suit yourself and to put the lure where you want it. Start with short casts and work toward accuracy not distance. Set up a circle on the ground that is about 3 feet in diameter and stand back about 15 to 20 feet from it. Practice tossing a hookless lure into circle. As you improve, move further back. Then reduce the size of the loop. You will find that you will soon be getting the feel for casting the closed face reel.
The open face reel is a bit more complicated to cast because it lacks the brake button. It has a "bale" or curved steel rod on the front that guides the line from the reel and back onto it as you reel it in. To cast, you use the indes finger of your casting hand (the one holding the rod) and hook the tip of the finger over the line coming from the reel. Then using the free hand, withdraw the bale into the cocked position whiloe continuing to hold the line with the tip of your finger. As you cast the rod forward, you slip the line off your finger just as the rod reaches the foremost position of your cast. This will allow the line to freely spool off the reel. To recover the line, transfer the rod to your freen hand and crank the rod with your casting hand. Some rods can be set up so that you can crank with your freen hand and nnot have to shift the rod from one hand to the other.
Bait casting....... nnow here is the most difficult type of reel to cast. Not impossible by any streach of the imagination but it requires a lot of concentration and attention to detail. It also requires a bit of coordination to keep things running smoothly. When casting the bait casting reel, you place your thumb on top of the line on the reel, release the brake on the side fo the reel as you continue to hold your thumb on the top of the reel to contain the line. As you bring the rod to the foremost position of your cast, you release the line with your thumb allowing the reel to free spool out the line. As the lure reaches the water, you will need to use your thumb to "feather" or gently apply the brakes to the spinning reel. Do not clamp your thumb down and suddenly stop the line but apply only enough braking force to keep the reel from spinning faster than the line is being puled off it. If you don't apply the braking force with your thumb, the reel will over speed the line and cause a teriffic tangle that we refer to as "building a bird's nest". The tangle closely resembles a bird's nest and is about as easy to untangle as a bird's nest. Many is the angler who has thrown his rod and reel into the drink in frustration over causing these extremely frustrating tangles.
So, I have covered the basics of casting with the various types of equipment. What I have told you will not be enough to make you a proficient fisherman. What I recommend is that you go to your local sporting goods store and inquire about lessons. You can cut a LOT of time off your learning curve and save yourself MUCH frustration by getting some hands on instruction.
Don't give up. Fishing provides too much enjoyment once you get the hang of a few simple skills. Heck, look at all of the people out there fishing. They once started where you are and they learned how to do it. If they did, so can you and then a world of fun will open to you. Not to mention the delicious fish you will be putting on your table.