The <p> tag was one example of a tag that doesn't have a separate "open" and "close". Another example is the <img> tag.

Have a look at the code below -- I've added a picture of my most-feared caterpillar.

The <img> tag needs some way of knowing what image it's supposed to display, and this is done using an extra bit inside the tag called an src parameter (parameter means "extra bit") that shows the web address to get the image from.

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It's pretty important to get the web address (also called a "url") perfectly correct, just like any other web address.

If you can't paste it into the address bar of your browser (the bit that starts "http://.."), then it's not going to work in a web page.