Sram in the ARM cortex m3
Since your microcontroller has an external memory controller, I imagine the SRAM would be mapped directly onto the main address space. The memory map in the datasheet shows that 0x60000000 to 0x6fffffff is reserved for external SRAM (look for "FSMC" which is ST's name for their memory controller). This means that once properly configured, the MCU can access the external SRAM just like any other memory.

You can tell the linker where to locate variables and data using a configuration file. In IAR, such a file would end in .icf and are often found under the project directory. If you are using a development board, and the project you're loading is an example for that particular board, then the linker file may already be configured to place read/write data in the external SRAM.