I haven't done one in years but no doubt others with specific and up to date advice will turn up shortly but in the mean time .....
It is quite easy. Sign up for a hosting package with someone like 1&1. A basic business package can be had for about a tenner a month or less, depending on your needs. You select a template, select stock photos, enter your text and publish.
Obviously if you want something more sophisticated then then you might need to buy your own software.
I'm starting my own business, after maternity leave and a good deal of procrastination, and I need a website. I'd vaguely thought I'd be able to do it myself, using clever intuitive software...but it's going to be harder than that, isnt it?
Im embarrassed by how little I know. Any advice would be very gratefully received.