Yeah ok so if i was using my ethernet board witch has a sd card reader that saves to a datalogger and a tft lcd that has it own SD reader that use it for its own bmp files how can this work if i can even do it
Each SPI device needs its own SS (slave select) pin. The Ethernet shield uses pin 10 as the SS pin. The SD card on the Ethernet shield uses pin 4 as the SS pin. You need to look at the documentation or schematics for the TFT's SD card to determine its SS pin.
In the SD.begin() call, specify the SS pin that activates the device you want to write to/read from.