Under Settings → Tax you set your tax rate, its label (for example “VAT 20%”), and whether your prices already include tax.
Tax-inclusive vs exclusive
If your prices include tax, Trayder shows the tax portion within the total. If they don’t, tax is added on top. Either way the customer sees a clear breakdown.
UK CIS (Construction Industry Scheme)
If you enable CIS, the labour portion of an invoice has the CIS deduction applied (ex-VAT, the correct legal base) and the customer pays the amount net of it, with a statutory note on the invoice. Mark material lines so they’re excluded from the labour base.