How do i use TX/RX (0 and 1) pins???

Hello guys,
I've already used all digital pins in my arduino uno, except for pins 1 and 0, but now i need to use them, but every time i try to upload a program using these pins, i get errors involving COM3, avrdude, etc..

I know that these problems happens because they are used by the board to communicate with the PC, does that means i can't use them in my projects??

Thanks

When you upload they must be disconnected, but once uploaded, you can connect whatever you have connected to them.

Ok, i did that, but since then, i just can't upload sketches to arduino, i'm completely lost and worried. Is there a way of cleaning the arduino sketch without using the computer?

Dont worry, I think I know whats happening. You configured pin 0 and 1 do to something and now they can get in sync with the com port. Ive been there lots of times. What I do is to manual reset the Arduino just before the code is uploading.
There's another option, to reflash bootloader with another arduino or programmer.