The analysis model describes the structure of the system or application that you are modeling. It consists of class diagrams and sequence diagrams that describe the logical implementation of the functional requirements that you identified in the use case model.
The analysis model identifies the main classes in the system and contains a set of use case realizations that describe how the system will be built. Class diagrams describes the static structure of the system by using stereotypes to model the functional parts of the system. Sequence diagrams realize the use cases by describing the flow of events in the use cases when they are executed. These use case realizations model how the parts of the system interact within the context of a specific use case.
You can think of the analysis model as the foundation of the design model since it describes the logical structure of the system, but not how it will be implemented.