I am new to this world and trying.
one question i am unclear is when you have a UNO and ethernet shield together and when your uploading the code via IDE do you choose Ethernet device or just UNO as a source to upload the code? and is it a must to have a micro-SD card? or the boards have small storage?
You would be uploading code to the Uno, so you select that device as the destination for your code. It is possible you need to disconnect any shields you have connected in order for upload to be successful, but that depends on the shield design and whether it interferes with uploads. There are different versions of Uno boards, and they all have storage onboard. Depending on how much you want to store, you may store your data using separate SD card storage, or use the microcontroller’s onboard flash memory or EEPROM memory.
thank you