UK Resident exploring freelance work for a Swiss Company
You will need to register as self-employed aka sole trader (that's the whole point: pay taxes on income that you're not getting as wages from an employer, who would arrange PAYE/NI contributions), or set up a limited company (in the last case you would have the option of either getting paid as wages or as dividends — which one is better is a complex issue which varies from year to year). You'll find lots of advice on the HMRC website.