What does it look like?
Malware can come in many shapes and sizes, some common examples are Trojan Horse, Viruses, and Spyware. A Trojan Horse is a file that seems legit, but once downloaded acts as an access pathway for other viruses and things to get onto your computer. Viruses are bits of software that are spread from computer to computer, usually through emails. Spyware is malware that records personal information on your computer.
How to avoid malware:
There are programs that you can download and run on your computer like Antivirus software and firewalls that help to block and alert you to spyware. Also, just use common sense when downloading a file.