I agree with Dave that your question is pretty vague.
What is "software architecture?". IF the question is about the operating system, it could be interpreted in a broad sense to mean 32-bit or 64-bit. But "architecture" includes a lot more that its 'bit-ness.' Explain the context of your question. Is this about operating system? Application? Architecture in regards to software is very similar to architecture in any discipline. It means "the complex or carefully designed structure of something."
General description of "client server." Again, pretty vague. So a vague response would be a server that is configure to offer services for clients. This could be a file server that serves as a location for client files. This could be a mail server that provides mail services for clients. This could be a web server that provides web services for clients.
The 'pros' to a client server is that an application can be installed on a server and provided to the clients instead of installing the application on every client device. One place to maintain a service instead of 10's or 100's or 1000's of locations.