One of the easiest ways to misery is being tricked into clicking a link in the wrong email. Many spam messages will have links, that if clicked, will end up installing viruses or malware on your computer. These fall under the "phishing" category.
There are some legit messages you might receive from companies like PayPal that will have a button or link they want you to click to confirm something or login, but unless you're absolute sure the email is safe (for example, if it arrives right after you did something on a site to trigger it being sent to you) it's always much better to go directly to a website and log in by hand.
Here's a new species of phish (I don't think anyone really refers to them that way though) that I found in my spam folder today...
There's several red flags to note:
Always trust your gut when you're unsure if an email is legit, and definitely always hesitate before clicking. You don't have to see anything happen after a click to be at risk.