There are a lot of ways to add patterns in Illustrator. You can use the Pathfinder tool, or you can use the Pattern tool. The Pattern tool is a great way to add repeating patterns. You can also use it to create logos, illustrations, and other designs. To use the Pattern tool, first open the Pattern tool palette in Illustrator. Then, click on one of the pattern pieces you want to create. The Pattern tool will start creating a pattern on the canvas. You can change the size of the pattern, and you can also change how many times the pattern appears. To finish creating your pattern, click on OK. The Pattern tool will close and return to its normal toolset.