Have a look at the getting started tutorial, it will take you through the process step by step of setting up a channel, getting data from another channel, and then processing and visualizing that data. After that short study, you should be ready to check out the device examples for an example based on the hardware you want to use. You will need some kind of device to read from the SD card, such as an Arduino, RPi, or some other processor.
The bulk update will let you send larger batches of data in one REST API call.