Search Engine Optimisation is very important and is the act of getting your website more visible in search engine results, and hence bringing more traffic to your site. There are various things that can help this process, such as making sure their is sufficent content on your site and it is all relevent to what your site is about, making sure it's responsive as this is now very important and if your site isn't mobile responsive it will become less visible in searches, the age of your URL and whether is contains keywords also matters as search engines will see if your URL has been around for a long time, or has been paid for for a few years instead of months then it'll seem more stable and secure. It's important to take this in to account when building a website so you can add suitable page descriptions and titles, and make sure you have a good use of meta tags.