Anyone who wants their computer to be secure but doesn't know how to start can benefit from guidelines on the Data Guard 365 website (data-guard365.com/resources/blogs/computer-security-its-bigger-than-spyware-and-viruses/).
Like a house or apartment, a computer has many points of entry. To keep out unwanted intruders you need firewalls and must keep updating your software. If the manufacturer does not install updates automatically, they should notify you they are available.
Subscribe to an anti-virus service that will install software and keep you posted on updates. When you get a notice, don't ignore it.
Finally, educate yourself on security developments, including new viruses and scams that are constantly arriving.