You can change the section title by editing the 'Heading' field. This is just plain text, so can't include any bold or italic text.
You can choose to show (or hide) the 'Title' for your Instagram block.
If you have set your Instagram URL in the 'Social media' section of 'General settings', the title will automatically link there.
The 'Access token' is needed by Envy to 'grab' the images from Instagram. There are full instructions on how to get yours here:
You can set the width of the Instagram block to either 'Full width', which will display the slideshow the full width of your site, or 'Fixed' which will display your Instagram images at the general width of your site.
The 'Remove padding' checkbox will remove all spacing around your images, so they appear as a single block of images.