[Custom] Theme Function Required

Hello,

I’m creating a vine website but I don’t understand how do I implement the vines on my website without any plugin.

As far as I know they don’t provide API at the moment for anything.

I would like to create a function something like YouTube embed videos.

I’ve saw in many theme they provide a custom filed area where we put the YouTube video id and it will fetch the video in the post and also get the featured image of that video.

Can anyone help me with this function for vine?

In the link below this guy created all the functions I think which I needed for my theme but I don’t understand how do I implement this on my theme.
http://wordpress.stackexchange.com/questions/129156/send-and-embed-vine-in-wp-post-on-facebook

I know the functions he shared will go in functions.php but how do I call this functions?

I’ve found another source for featured image maybe these can help us a little bit.
https://halgatewood.com/php-get-vine-app-video-thumbnail/