Viruses

Unknown

Hello, could anyone help me please?I don't understand anything about computers.I have several viruses, what should I do?I have the antivirus Avast at the moment.It will expire and I don't want to pay.Any recommedantion?First, any idea of what is happening in my laptop?I have been having the message from this Security Tool saying someone is trying to see my bank card details and when I want to remove the viruses, it gives the option of paying only.Sorry, hope any of this makes sense.
Thank you, hope to know from you soon.
Mar