Hi @Damien_Ross
Generally what's meant by expenses (known as 'Allowable Expenses') is approved categories of costs that you can use in your business that will reduce your profit.
For example, of your turnover was £40,000 and you had allowable expenses of £10,000, your taxable profit is only £30,000 - you would only need to pay tax on this.
I'm not an accountant, so it's always worth checking what is allowable and what isn't, but HMRC has a useful guide here that's worth checking out.
I hope that helps!