Issue when using laravel forge with bitbucket

When using bitbucket with forge, you have to follow this message in order to use bitbucket and forge

When using a custom Git deployment or Bitbucket, you must add the following SSH key to your source control provider before installing repositories:

The problem is this is not clear where do i put the ssh key, there's a million place in bitbucket that you could add a ssh key to so. so please can some one explain to me why when using bitbucket i need to add these ssh keys and where should i put them.

Some back story i was following a tutorial about deployment with forge and he used github and linked his repo with the forge Site, when i tried doing this using bitbucket it kept failing because the ssh of course it will fail, it need access to that repo by ssh. but how when using github you don't need ssh keys ?