如何在我的控制器的symfony供应商目录中使用第三方API

I am working with an existing controller in symfony and need to use an api that I have in my vendors directory. Needless to say I am entering a pre-existent, large scale project and with minimum experience in symfony I am not too sure of how to use the vendor directory. When I have tried using "use vendor\fullcontact\sdk*********;" symfony tells me that there is no class called this in my bundle. I have looked for information on using the vendor directory but have came up dry. Any information regarding how I can start using my vendor directory would be appreciated.I am working with an existing controller in sym