What goes on your documents, and what stays private: business details, UTR, payment details, VAT.
Settings has two blocks. Profile is you: name, email, phone, address. Business · on documents is what the client sees as the "From" on invoices and quotes: a business name if you trade under one, the business email, address and phone.
Enter your UTR and switch on Show UTR on documents: companies deducting CIS need it on the invoice. Your National Insurance number is kept for your records only and never prints on anything a client sees.
Bank name, sort code, account number and the reference you want clients to use. They print on every invoice under the total, so nobody has to email you for them.
A UK limited company adds its company number. VAT registered? Add the VAT number and rate, and invoices show VAT on top. The CIS rate (20% or 30%) lives here too and becomes the default on invoices.
Pick the colour that tints your documents and add a logo; the PDF the client opens carries both.
Related: VAT and CIS on invoices, your first invoice, security and your data.