To explain the importance of the Search Engine Optimization, here is a real-life example.

John is a mechanic who lives in London and works only with sports cars; he has a garage called “John’s Garage”.
He has a company website that hasn’t changed for five years; he uses it as a way to make people find him.
The only way to find him online is to Google “John’s Garage” and scroll down the page until you recognise his website, and you’ll often only find his page on a PC, because his website isn’t responsive and definitely isn’t designed for mobile users, such as smartphones and tablets.

Ten years ago John was the best in town, but David is slowly taking all of his customers…and he doesn’t understand how!

David also owns a garage and is a direct competitor of John.
His website is optimised, and up to date, he always uploads pictures of his latest jobs, and he has created an audience that follows him on social media.
With that, he already brings more people to his business, but David is even smarter.

David has hired a freelance web designer and SEO expert that delivers monthly updates to his website and SEO.
After five months, typing in keywords into a search engine such as “Sports Car Mechanic London” “Gear mechanic London” “CPU Remapping near London,” and his website appears on the first page.
90% of web users, will only click on websites that are on the first page of search results. If you are not on the first page, you are missing out.
Now David’s website has the visibility that converts browsers into customers.

To keep up this business growth, he reinvests his money into online advertising to further enhance his website.

Depends on the platform that you decide to use, if you choose WordPress or Shopify then yes, it is easy to make the changes yourself.