In addition to being standard digital pins, pins 0 and 1 have hardware serial communication capability. The RX stands for "receive" the TX stands for "transmit". On most of the AVR-based Arduino boards (e.g. Uno, Mega, Nano, Pro Mini), these pins are used for uploading sketches to your board and also for communication with the Serial Monitor. On the native USB boards like Leonardo, pro micro, etc. pins 0 and 1 are still hardware serial but they are not used for communication with the computer. Connecting things to pins 0 and 1 on the non-native USB boards like your Uno can interfere with serial communication with the computer and cause you to not be able to upload sketches so it's usually best to leave them alone. It is possible to use them as standard digital pins as long as you aren't also using Serial.
Did you know that the pins A0-A5 can be used as digital pins as well as analog inputs? If you haven't used all of those pins up then I recommend using them instead of 0 and 1.