It depends on your weight, how far along the puberty line you are, what your requirements are and what your diet is already like. Eg I get horrible period pains, I take certain vitamins to help. I also eat alot of green vegetables every day and chicken or ham so I don't take iron as I don't need it.
Try to work out why you need the vitamins, then look into if they are helping you if you are concerned, but if you are OK with taking them theres no reason to stop. Ask your mum why she gives them to you.
Also depends on what your aims are. Pills are never going to have you lose weight or gain muscle, food does that, vitamins can help with cravings, can take the edge of low energy levels or can amend issues that people such as vegetarians may have through lack of certain foods.
Personally, I like to see what my body lacks then add the vitamin rather then the other way around. If you eat a healthy balanced diet with now or a low amount of cr@p then unless something isn't working properly, its unlikely you will really desperatly need certain vitamins, but like I said, if you find your OK with taking them, keep doing so.
Google each of them for more info on what they do, Wiki has a long list which is better to read then to post the whole thing on here.