Not a car person. Are you? if so please answer!?

Ok...so i need new struts. latley my car has been whobbling a lot more and stuff (thats the struts right?) and my mechanic said i need new struts. so today i got down and looked at the front end of my car and theres this circle thing hanging off. it says "violent clip-23" or something like that on it. i dont know what tthe hell this is. do you ???? its a small circle like thing behind the front tire. its just hanging by some rubber i think. help??