A new website is like a house nobody knows who lives there and also the person who is living in that house his friends and relatives also don't know what is that person’s address, so if you have settled in new home you need to tell your close one and your neighbours your name and this is your new address.
Same as above is the case of new website, you got a website but no one knows you have a website, it can’t give you benefit of increase in sales for which you got it registered until you ask a SEO agency to perform SEO for your new website, SEO service will make your website visible on top pages of SERP with desired keywords, when the website will be on top SERP, it will be visible to people when they search with those same keywords, so it's going to attract more and more organic traffic on website, which can be converted to sales.
To know more on benefits of SEO for new websites follow the link mentioned below.
https://www.algosaga.com/blog/seo-for-new-website/