A transaction performs a series of reads and writes "atomically" i.e. as if they were done all at once. If anything is failed in between, all the actions will be rolled back to original position.

Transation time is nothing but the total time taken to complete a transation ( set of actions - it can be a combination of reads and writes from or on to a database)

Where as the Server response time is the time taken by the server to send the response back to user/application. Typical example is - when you click on the Log On button in any web page - the browser sends a request to the server. Server process the request and takes the appropriate action based on the request parameters and sends back the response to the user.
The time taken by the server to process the request and sends back the response to you (or browser or any other application) is nothing but the Server Response Time.

Thanks
V.Vadivelan