Virus Vs Trojan

It is easy to confuse the terms virus and trojan horse. A trojan horse is not a virus. A virus is software that has bad intentions and can recreate itself and a trojan horse is a type of file that needs to be downloaded in order to work.
Sometimes, a trojan horse will disguise itself in a folder or music file while in fact, it's an executable file. This is to trick the users so they will click and execute it.
After the computer goer downloaded the file, it will open a black hole for dangerous software such as spyware, adware, and other keyloggers to infect your PC. Keyloggers are pieces of software that can record whatever you send the information such as username and password to another third party for their own purpose.
So, how actually people can get infected by this malicious software?
Usually, people who get infected actually downloaded the program themselves or it's being downloaded into their system stealthily. For example, you want to find paid software that can convert a video format and you search it on Google.
Some of the websites from the search results provide the download for free. This websites however never offer the download for the genuine software. Instead, they will upload trojan horses to their websites for you to download.
So, you download this software into your PC and thinking that it's the genuine software and execute it. This software then creates a backdoor for other malicious software to break into your PC.
How can you prevent your PC from being infected?
In order to prevent you from getting infected by this type of malicious software, what you need to do is you need to do a research first before actually download it. Google it first to make sure that it's safe. If it's not, you'll find a lot of results from Google mentioning that the software or the website is malicious.
If you know the size of the software, it would be better. For example, let's say the software size is supposed to be 100 MB but in that website, the size is 100 KB. This is most likely malicious software. So don't download it.
This is just an example. The main point is, what you need is knowledge. Knowledge is very important in fighting online threats. So, learn what you can and apply it to protect yourself and your PC.