I think this very much depends on your age and the type of relationship you have with your parents. I'm going to presume you are a young witch with this question and live in your parents home.
Sometimes parents may not understand the difference between the different Pagan religions and may not understand exactly what witchcraft involves. Witchcraft can also be confused with Satanism and such associations may well not help your cause. The best thing to do with regard to your parents is to be honest with them. Talk about why you want to be a witch and what elements of the craft appeal to you. If your parents are open minded, perhaps lend them a book on the subject and ask them to read it and discuss their thoughts with you afterwards. If your parents voice objections, stay calm and try to understand exactly what it is they are objecting to. Be prepared to compromise, if your parents do not want you lighting candles in your bedroom or using a Ouija board, find other ways that you can agree on to practice the craft. There are many different ways of adapting and interpreting the craft - this is what being a witch is all about. Use your imagination for substitutions that both satisfy your needs as a magical practitioner and retain harmony in your household.
If your parents have strong objections and no compromise can be reached then you may have to consider putting actual practise of the craft on hold until you have your own place.
It is important to remember that while you are in your parents home they have the right to ask you not to do anything that they would consider offensive. If your parents follow a strong faith of their own, they may disapprove of witchcraft. Even after reasoned discussion they may still disapprove of witchcraft. There is no reason you cannot use the interim period to read and learn as much as you can but I believe it is important that you do not lie to your parents as to do so would be compromising your personal integrity and would have a negative impact on your magic anyway.
Be prepared for the likeliness that your parents will consider this to be a phase. You know, that isn't a bad thing. We will all go through many phases in our lives, we try different things as we journey toward feeling what is right for us. Don't take it as an insult, if witchcraft is right for you then you will prove it in the fullness of time. If it isn't for you, studying it will be another valuable experience that goes into making you. It isn't an insult to say we go through phases in our lives, you more you try and the more you experiment, the more you learn and grow as a person.
Good Luck x
Image http://www.sxc.hu/browse.phtml?f=view&id=1193454 (donzeladef)
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