Trademarks are words, phrases or symbols used by individuals or businesses to identify their products and to distinguish them from their competitors. You see trademarks all the time; some familiar trademarks are "Just Do It" for Nike and the apple used on Macintosh (now Apple or roughly referred to as Mac) computers.
Sometimes, trademarks can include colors or packaging, if the product warrants it. For instance, the shape of a Coca-Cola bottle is an identifying feature and is protected by law. Specifically, this kind of feature is known as a "trade dress" and will be protected if consumers identify a manufacturer due to the color or shape specifically. The only catch is that the feature may not provide a functional advantage. If it isn't solely a cosmetic look, then it's not protected under trademark or trade dress law.
Trademarks make it easier for consumers to identify the things they want and the manufacturers they want those items from. For example, if you specifically want to purchase Adidas shoes, you'll look for a three-striped set of leaves or what appears as a three-striped mountain. Specifically, the three stripes are an identifying mark for the company. This helps, because a consumer knows that a two-stripe version is not from Adidas, just as the swoosh symbol is a representation of Nike instead.
Trademarks fall under federal law and may not be used without permission from the owner. If your trademark is used or infringed upon, you may be able to hold the other party responsible and seek compensation for any losses that you've suffered.
Source: Harvard.edu, "Overview of Trademark Law," accessed May 18, 2018