First off, well done on the new job!
It all sounds like quite a lot for a first day, was your line manager or a supervisor there for it? I'd recommend speaking to a manager/supervisor about your concerns regarding the documents - I imagine they are guidelines for OTC protocol, safeguarding, GDPR etc if you are working as an advisor. It's tremendously important that you're familiarised with all guidelines for medications, common drug interactions and also how to spot a potential safeguarding case should it arise. There is a lot of information for a reason and like you said, handling medication is a big responsibility so don't just go along with things because you're being hurried - you don't want to sell Night Nurse to someone already taking Lemsip at bedtime, or Nurofen and Calpol to the parent of an infant who hasn't sought medical advice. Familiarise yourself with the BNF and common interactions.
Don't let the first day put you off, rarely is the first day on the job indicative of what it will be like further along. When you go in for your next shift, speak to a supervisor and express your concerns re: learning and policy for that branch specifically, ask them for any tips that they may have for someone just getting started and perhaps suggest shadowing a colleague for half a shift so that you can familiarise yourself with procedures. They won't expect you to know how to do the job immediately unless you've come from a long stint in Pharmacy elsewhere, so stick with it, Pharmacy was what got me started on the path I am on now and it certainly taught me a lot.
In terms of workload, multitasking etc unfortunately that's what Pharmacy is like a majority of the time, retail and NHS will more often than not involve being asked to do tasks other than your 'own'. If you don't have much experience in the field it can certainly seem chaotic and dangerous, but if they are familiar with what they need to do and everything is carried out according to policy then doing several things at once is just part of this line of work. Obviously if you see something unsafe such as controlled drugs not being handled correctly or breach of data then you need to raise that concern immediately with a senior staff member but on the whole, yes it is usually a busy and often chaotic environment but that's part of the charm.
Feel free to give me a shout if you want to know or talk about anything!