ive been working in a pharmacy for about 18 months now, and before that i had NEVER had any sort of job...
its pretty simple, at first they'll probably just put u on the counter where prescriptions arent dispensed, while you get used to it...
ie. while you learn where abouts all the products are on the shelves, how to operate the cash registers, how to interact with customers etc (on your first couple of days another staff member will probably stay with you and help u to do everything, thats what happened for me) any customer complaints, just get the manager to deal with them
then you'll start to learn things like how to transfer a sale to a customers account, how to do laybys, how to get a customer's medication up on the cash register so they can pay for it, how to answer the phone, then maybe even learn to take special orders or arrange hires for wheelchairs, crutches etc. and dont worry, someone will teach you how to do all of that!
once your used to most of that ^^ they'll probably place you at the main registers where customers put their prescriptions in & pay for them. someone will teach you how to take in scripts for the pharmacist to fill, and then once the pharmacist has finished it, how to sell it to the customer. you will also learn what to do when a customer asks for a behind the counter medication, and also how to record sales of drugs with pseudoephidrine in them (ie. over the counter cold and flu tablets).
the next stage is pretty much just helping customers choose generic products (eg. makeup, skin care, bandages etc), you'll be able to do that as you gain experience and get familiarised with the products and what theyre for etc.
the main thing is not to stress, and dont be afraid to ask fellow staff or your manager for help if you need it. you will always be shown how to do new things before you actually have to do it. 18 months on, and im pretty confident in all the things i just mentioned (except crutches hire lol) yet im still learning... if i dont know how to do something though, its not a problem, i just ask another staff member and if they dont know, i just ask one of the pharmacists or manager
also, if you're ever unsure about any aspect of a medicine, its VERY important to ask the pharmacist. i still do this for any medicines im not sure about, even if its something as simple as a vitamin or panadol.
im 17, my position is also pharmacy assistant, and im a casual... i get about $13.30 an hour
your hourly wage might be lower than this if ur part time, and also you tend to get a lower wage during the first 6 months.
just keep your cool, act professional as possible when making a sale, and try to be confident when dealing with customers/staff.
good luck