Should i learn WCF, after finish web api

I am building E-Commerce web software using Gang of four pattern design. But I have confused about Enterprise Pattern Design.

In my project exist BLL/DAL/ServiceLayer using SOA and presentation layer. But I have confused about Web API. What is the difference between WCF and Web API? Using Gang of four pattern design is suitable for building large web software? Is service layer SOA same as Web API? Please help me sir I am facing so very confused