When it comes to these principles like architecture and Infrastructure how would you describe them? The actual meaning and in development where its used. So for example is it like infrastructure is the actual website and architecture is the plans or so called blue prints (UML) in the background?
Infrastructure is a word used for the underlying components that support the operation of something. In your example, you said a "web site" - so things like load balancers, web servers, database servers, and the operating systems that run those servers would be included in the infrastructure. This can go more granular, to include the details of the data centers that the servers operate in. [power generators, cooling, etc.]
You are correct in that architecture is use to speak of the "blue prints", or the design of something. UML, which you mentioned, is one way to express and visualize a design. It tries to answer questions like: What are the components? What are the relationships between the components? What do they do, and not do?