Search Engine Optimisation
It's easy to build a website. But that doesn't mean people will find it through search engines. Your site may need an SEO to perform Search Engine Optimisation.
Keyword Research
The first and most important step is keyword research. You need to find out what people are actually searching for, relevant to your subject. Google provides numerous free tools enabling keyword research, including search statistics by industry, search trends, keyword search volumes and how competitive those keywords are.
There are other tools that will show which keywords your competitors are ranking for, and what words they are paying for, through Paid Search, such as Google AdWords.
Based on this keyword research, you can then decide which keywords to optimise your website for.
Content
Content is King. Search engines love pages with lots of content on them - it makes it easy to work out what the page is about. Each page of your site should ideally be optimised for one or two keywords. Then you should use those keywords on the page title, meta tags, headings, text content, image alt tags, bold or italic text - but don't overdo it. Search engines don't reward pages that are stuffed with keywords - they consider it spam. Just talk naturally on your site, and provide useful information.
Structure
You also need to make sure your site is structured well. That search engine programs (also known as spiders, or robots), can follow links on your site. That you're not making it hard for the spiders to follow links, by using unncessary redirects, hiding parts of your site via a robots.txt file, having unnecessary formatting or coding making your page too big.
Links
Search engines, especially Google, see links from other sites to yours as a vote of popularity. If an authority site on your subject links to your site, using a text link that includes your keywords, and is surrounded by other related information, that can give your site a tremendous boost in position for searches for that keyword. The hard part is obtaining a decent quantity of quality incoming links.