C's are not bad but there is obviously room for improvement. Grades today are highly inflated. C's use to be average but not anymore. If you have intentions of going to college, you'll need to step it up a bit. Get a tutor or extra help if you need it. Now's the time to make that adjustment - not later.
If you have trouble learning, try speaking to your guidance counselor. They should be able to direct you to a tutor or a class that deals with students with learning problems. Everyone can learn, some just need to be taught in a different manner than others.
Isn't as bad as some people make it out to be, but improvement is possible. Seek tutoring, and take what you learned during that day and keep studying and practicing to get better. Sometimes the trouble isn't always learning. The teacher also needs to know how to break things down to a better understanding because not everyone would get it the first time around.
I don't know if the C you are earning means you are learning a lot of the information in your classes or if it is an inflated grade. When I earned Cs, it meant I really didn't understand the subject as well as I should. If you are doing all the work, studying for and passing tests, doing a decent job on papers, doing turning in all the homework and asking for help when you are confused, you are probably doing as well as you can. Sometimes reading ahead or learning the vocabulary for a chapter that will come up in a day or so can give you a better understanding because you already know the terms that will be discussed. Sometimes reading other material on the same subject can make it clearer. You need to get ahead in the subject rather than always trying to figure out things after the have been presented.
Not necesssarily, you may not like the teacher just so, or you are a shy kid in Public Speaking class. The grades you get, if worked at, are yours, and you should be proud of them. You did! Remember, some kids fail, and I knew an instructor that put "loaded" questions on tests, nobody got a "perfect" grade. If you want to try harder, get a (better graded) student tudor, or ask the teacher for help.