How to add share button to Magento

You can use share this tool. This will give you icons and sharing links. For sample I have added code here. You can also generate new using this which is free and open source,
Copy the span tags and place them where you want your buttons to appear in the code.

span class='st_' displayText=''></span>
<span class='st_instagram' displayText='Instagram Badge'></span>

Copy the script tags and place them inside and at the end of your “head” tag.

<script type="text/javascript" src=""></script>
<script type="text/javascript">stLight.options({publisher: "791bb30f-74a2-4e0f-bde5-5bc23d04c358", doNotHash: false, doNotCopy: false, hashAddressBar: false});</script>

For the WooCommerce I use 

Instagram Followers Shortcode

I also recommend this plugin to convert your Wocommerce website into Instagram shop.