There are two techniques for dating in archaeological sites: relative and absolute dating.Relative dating stems from the idea that something is younger or older relative to something else.
If you hear of a carbon dating up in the millions of years, you're hearing a confused report. Second, they rarely contain any of the original carbon.
We can't date oil paints, because their oil is "old" carbon from petroleum. And third, it is common to soak new-found fossils in a preservative, such as shellac.
Three isotopes of carbon are found in nature; carbon-12, carbon-13 and carbon-14.
Carbon-12 accounts for ~99.8 % of all carbon atoms, carbon-13 accounts for ~1% of carbon atoms while ~1 in every 1 billion carbon atoms is carbon-14.
When it comes to dating archaeological samples, several timescale problems arise.
For example, Christian time counts the birth of Christ as the beginning, AD 1 (Anno Domini); everything that occurred before Christ is counted backwards from AD as BC (Before Christ).
The C14 will undergo radioactive decay, and after 5730 years, half of it will be gone. So, if we find such a body, the amount of C14 in it will tell us how long ago it was alive. The method doesn't work on things which didn't get their carbon from the air.
This leaves out aquatic creatures, since their carbon might (for example) come from dissolved carbonate rock.
The Mayan calendar used 3114 BC as their reference.
More recently is the radiocarbon date of 1950 AD or before present, BP.
Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.