How do I hand in my notice?

Basically you should have signed a contract upon starting work that detailed the period of notice that you have to give to quit - it's normally around four weeks but in part-time jobs it can be as little as a week.

The best way to do it is to write out a letter expressing that this is your notice and giving the date at which your notice would end starting from the date you hand in the letter. Explain your reasons if they are not too personal and always remember to thank the shop (and your colleagues) for the opportunity (bit corny I know but its good practice.) Also include your contact details in the top right hand corner.

Then all you have to do is hand it in. It can be awkward but many people have done it before and I've never had a problem with anyone I've worked with.

The Christmas thing is tricky as you are leaving them at a bad time. If you feel that you can't do that then stay til after Christmas but that's up to you. They cannot make you work beyond the terms of your contract, including notice period.

Hope that helps!