Although this website has its own search box, you might find that Google works better. If you want Google to search within one website, just write the word or phrase that you want to search for, followed by "site:URL".
For example, here's a search for "environment" on this website:
Here's a search for the phrase "in terms of". Notice that you need to use speech marks to search for a phrase:
Try doing both searches. The results that Google gives you should come only from ielts-simon.com. Can you see why this type of search might be useful?