Intellectual property is a legal ownership, of an abstract artistic creation, symbol, or a physical implementation of an idea. These types of property are protected, by laws like physical goods and services. The value of intellectual property is not primarily in the physical manifestation, of one physical, or digital item or copy. The value is in that information that the item contains, where the reproduction is only a minor part, of the overal value, of the product or service.
Copyright is the most commonly talked about intellectual property, in the artist and entertainment industries, which is a legal protection for a creative work, including artwork, video, buildings, writings, and computer code. The work does not have to be artistic in nature, just that it is a unique type of media, that was created. Designs and specifically fonts are deliberately excluded from protections, unless you do a really precise copy of someones designs and fonts are protected, by something called and End User License Agreement.
The ethical principle behind copyright law is very simple: do not use anything that you do not have explicit approval for. You often have to pay different amounts, for different uses, like fonts can be licensed, for websites or just for using, in graphics, or embedding in PDFs. Rights for things like immoral activities or things that make the author look bad have to be negotiated separately. Using media without approval is often called piracy, which is just a fancy euphemism, for stealing.
Royalty Free Media
If you need photos or drawings, you can usually buy things called clipart, stock photos, and royalty free media, where you buy one picture or sound or whatever, for a set fee. You can then you can use it, in anything, that the license allows. You can use repeatedly, as many times as you want without paying anything more, than you did, with the initial fee.