Overstaying the Visa Waiver Program means that you will face more difficulty trying to return to the US. You will be ineligible for the Visa Waiver Program in the future, because you overstayed. You will have to apply for a B-2 visitor visa to visit the US.
The B-2 tourist visa has an application process and fees that you must pay at the US consulate in your home country. As part of the application process you have to prove that you do not have immigrant intent (you are not coming to the US to live).
If you overstay the time that you were given on the visa waiver program you will start accruing unlawful presence. You may be barred from returning to the US for 3 or 10 years depending on your length of overstay. Click here for more information on the 3 or 10 year bars.
If you have overstayed your authorized stay in the US, VWP travelers have less immigration relief available to them than do travelers that came with a visa. For instance, if you had received a B-2 visa you would be able to apply to extend your stay. You cannot extend your stay as a VWP visitor, unless you have a true emergency situation (ex. medical emergency). You may be eligible to apply for asylum, but you should speak to an immigration lawyer about making an asylum claim. Feel free to contact me if you have any questions about adjusting status in the US or returning to the US.