It depends. SEO is most likely easier than you think. However, you should not underestimate the amount of time, effort and investment that it will take to run a successful SEO campaign. Ranking for any reasonably competitive keywords will take hard work and you will have to spend more than just a few minutes here and there to see long-term success.
SEO is as easy as making sure that Google sees your website as a better and more relevant result to rank for your target keywords than any of your competitors websites. This is usually easier said than done which is why a good SEO company can save you time, stress and money.
Making your website better than your competitors websites will involve improving your content, addressing any technical SEO issues on the site and building your reputation online (through earning links and mentions from other high-quailty and powerful websites).