Enzo954,
Search engine optimization is a very big world and there are many things to learn however the best place to start would be with target keywords for your website. Choose the keywords and their variations that you want to include so searchers can find your content.
You will want to include these keywords in the content on your website as well as the architecture of the website (meta tags, alt tags, and titles). Choose keywords that are important to the product or service you are marketing and build a page around each one. There are certain characteristics as to how you do this such as keyword density in website copy and the number of relevant keywords you should include in meta tags.
Another thing you can do to start is learn about what white hat and black hat SEO are and their differences. Depending on what you want to accomplish, there are some tactics that may not be good to practice.
The tasks mentioned above are known as internal or onsite SEO and are related to website architecture that you have direct control over. Another aspect is offsite SEO which can include creation of external web properties that contain target keywords, article marketing and syndication, optimization of video, document sharing, link building and a number of other tactics.
It would also be wise to follow industry leaders in SEO to help guide you to good information on the subject. Keep up to date on industry news by reading the blogs and following the social media accounts of industry leaders. SEOMoz is a good one along with @randfish - Rand Fishkin the organization's founder. Another good resource is SearchEngineLand.com and you could follow @DannySullivan - Danny Sullivan, the website's Editor. Matt Cutts -- @mattcutts who is head of the webspam team at Google is another great resource.
Here are links to more information on SEO to get you started,
http://www.seomoz.org/learn-seo
http://www.seomoz.org/blog/the-beginners-checklist-for-learning-seo
http://www.hubspot.com/learning-seo-from-experts-guide/
Hope this helps you,
Shawn