Malware can get into your computer when you are downloading something that contains malware in it, but you don't know it.
Malware can steal personal information, such as info for your social media accounts like your password or email, or gain your bank account details.
To make sure that you are safe from any type of malware, you should scan your computer storage devices with an antivirus daily and be careful what you download and from where, as some websites main goal is to spread their malware by lying about what you download.
You can even get malware by connecting to some websites. Some websites want to spread their malware, so if you happen to connect to a website for whatever reason, your computer might be getting infected by malware. Usually some antiviruses can detect whether or not the website is safe and if it ain't, it usually recommends you to leave that website.