i haven't actively worked in a store since the late 80's, but i'm still in retail, so some of what i write maybe slightly out of date, but...almost all companies have their jobs posted online and will ask you to fill out an online job application. even for their professional jobs. you can walk in, and maybe talk to someone, but your still going to have to go thru the online process. many stores will only schedule interviews for limited days or times because they need to schedule the current staff around the fact at least 1 person will be off the floor.
there are different kinds of retail environments and depending on which one you are applying to will dictate what to empathize. are you looking at a shop that wants/expects you to sell and project a knowledge of what you are selling (in the US think Nordstroms) or are you applying to a store that expects you to keep the store clean and stocked (in the US think Walmart/Target) or are you applying to a store that wants something in between (in the US think Banana Republic etc). for stores like Nordstroms etc its about prior retail jobs, knowledge of fashion/what you are selling, and how you present yourself. for places like Walmart/Target its about reliability and flexability (will you show up and will you be able to handle different types of tasks). for stores like BR, honestly, some of it will depend on the current job situation in your city, ie how desperate are they for help, (or do they need you more than you need them).
i don't think anyone in chain stores really cares that those applying for sales positons know MS word or power point. as for working a registar, they are pretty much scan and touch screen, so your knowledge for the 80s isn't really relevant, expect to say that you've had experience helping customers complete their transactions.
hope this helped. good luck