It will not be possible for us to help you with that problem based on such a vague description. Please provide a detailed explanation of what you mean by this, including:
What did you do?
What were the results you expected from doing that?
What were the results you observed that did not match your expectations?
Make sure to include the full and exact text of any error or warning message you might have encountered.
This is normal and expected.
This is the usual behavior for a new board. It will cease to do that once you upload a sketch that does something other than blink that LED.
You can start by uploading the BareMinimum sketch:
The upload should finish successfully and the LED should no longer do the slow blink.
Now you can upload the Blink sketch:
This should cause the LED to blink again. You can change the delays in the sketch to get different blink rates and durations, upload again, and verify that the observed behavior matches what you expect from your code.