There's plenty of good antivirus software out there, and there's plenty, that while not that great, will still protect you. There is, however, plenty that doesn't actually met what we would consider the minimal levels of protection.

Avoid any antivirus software:

• That doesn't have real-time protection. Sometimes this is inaccurately called 'on-demand' scanning (Despite that being something else.), sometimes it's called 'on-access' scanning. Whatever it is, it means that files are scanned when they are launched or loaded into memory. Your AV software must have that.
• Without automatic definition updates. As we say on the configuration page, non-updated antivirus software is worthless.
• That doesn't let you scan an entire disk manually, or at scheduled intervals.
• That doesn't let you manually select and scan a file, usually via a the right-click content menu in Explorer.
• That doesn't present detailed information about viruses found.