Someone on one of our cousin websites had a similar concern:
Point is, don't worry. If you're interested in puzzles, you belong here. You shouldn't be surprised that you can't solve most of the puzzles here. If all the puzzles here were too easy, you wouldn't even remotely get a chance to answer before anyone else does it first. Personally, I rarely am able to answer a question, but when I do, I feel very accomplished! Don't let any one of those smart people that answer like every question discourage you.
Creating a good puzzle isn't easy either. If it was, we would have a ton of new questions every day. If you really want to create a nice puzzle for us, don't stress/rush it. As you go about your life, you might think of some nice puzzly ideas. Then, someday, you might combine some to make a cool puzzle. My first "good" puzzle on this site was heavily inspired by a handout I got in some math class on equivalent adjacency graphs of the United States, for example. So, unless you're a puzzling genius, be rest assured that the puzzling creating process is not immediate, and will take some time.
You don't even have to answer OR create puzzles if you want to contribute. If you come across a puzzle that you can't solve, it is common to ask it here and credit the source (provided that you check for duplicates first). In fact, over my two years contributing to PSE...
Don't let any competition stress you out. If you spend alot of time writing an answer and someone beats you, don't be afraid to post your answer anyway, especially if you put in alot of effort into it. E.g. Question 16 Ripple Effect
You don't have to completely answer a question either. If you have made some significant progress, you can post it as a partial answer. E.g. Introducing: Jormungand
If you come up with an answer to your own question (not an original creation), don't be afraid to self-answer. E.g. What is the strategy to solve Simon Tatham's Twiddle?
Lastly, alternative answers are ok too. E.g. Get 6 6 6 6 to equal 58
Good luck with your PSE endeavors!