How to pay for US tourist visa online?

The most convenient payment method for your nonimmigrant visa application (NIV) fee is online with a debit card.

Once you log into your profile and while on the payment screen, you can select to pay using a debit card.
After you pay the visa application fee, print your receipt for your records.

How long does it take to get a US tourist visa from UK?

Visa processing takes approximately 21 workdays from the date on which the application is received by the Embassy. A further 2-3 workdays should be allowed for the return of your passport.