Plea definitions are provided here for your reference:
Guilty - You admit you committed the act(s) for which you were charged. You admit the act you committed is prohibited by law and you have no legal defense for your actions.
Nolo Contendere / No Contest - You are not admitting or denying you committed the act(s) for which you were charged. This type of plea simply means you do not wish to contest the state's charge against you. You may be found guilty by the judge, but could still be eligible for deferred disposition or defensive driving.
Not Guilty - A plea of "not guilty" means that you are informing the Court that you deny guilt or that you have a good defense for your case.
When you enter a plea of Not Guilty to a charge, you will need to decide whether or not to hire an attorney to represent you. You may defend yourself, but no one other than an attorney may represent you. You must speak on your own behalf unless an attorney represents you. In the State of Texas, no individual other than the defendant may enter a plea on behalf of another individual (except in cases where an attorney is retained.) This applies to spouses and all other family members as well. A defendant must enter a plea on his/her own behalf.
If you choose to defend yourself, you are then set for a Pre-trial hearing. This is a mandatory hearing in which you are visiting with the Prosecutor about the case. If an agreement is not reached with the Prosecutor after the Pre-trial hearing has been attended, you are able to request a trial by Judge or a trial by jury.