These flags allow you to specify the formatting of your color target, and depth stencil buffers that are a part of the final frame buffer.
The color target is typically formatted in a R8G8B8A8 format, providing 8 bits of precision for each color, and the alpha channel. This gives a total of 32 bits.
The final two flags specify formatting for the depth stencil, this is typically formatted as D24S8, and this indicates 24 bits of precision for the depth buffer, and 8 bits for the stencil. Higher precision on the depth buffer allows for more accurate depth testing when checking for overdraw.
When the frame buffer targets are created, it will use these formatting specifiers to indicate to the rendering pipeline how to interpret the data when reading from and writing to it. These buffers are allocated in VRAM to provide faster access to the GPU.