There are three types of pleas:
NOT GUILTY: means you formally deny committing the crime of which you are accused. If you plea Not Guilty, your case will proceed towards a trial where the State must prove you guilty of the crime. You can change this plea at any time during the course of the Court case.
GUILTY: means you formally admit to committing the crime of which you are accused.
NO-CONTEST: means you do not admit to committing the crime nor do you deny committing the crime. Rather, you admit that the STate can prove the case against you.
For sentencing purposes, either a plea of Guilty or No-Contest will result in the same sentence.