You seem to be asking what a 'vat number' is.Have you received some bill, business or official document asking for your VAT ['value added tax'] number?
You only have a VAT number if you are a registered VAT business. You have to be registered if you have a turnover above a certain level.Once you are registered you charge all your customers VAT on the goods and services you provide.On the other hand, you deduct VAT you've been charged on goods and services you've had to buy to run your business.You then have to fill in a VAT return and send it to the VAT office and pay or receive the difference.
You may be asked for your VAT number in some business enquiries, as a matter of form.If you aren't registered you haven't got one to give (but ought to find out whether you have to be registered!)