1-From your Admin page, click on the icon with the 3 lines (hamburger button ☰) next to View your store, Store configurations>Store identity
2-From Store identity you can add your social media pages links by copying the page link and pasting it in the fields shown in the picture below.
3-At the end of the page, click on save changes.
4-You can view how your social links will look to your customers by clicking on View my store at the top of your store Admin control page.
5-In your store frontpage, scroll down till you find your homepage footer, and you will see your social media icons, that is how your customers can find them and can contact you.