I’d been arrested few days ago,because of I stolen some grocery in a grocery store (I did before but this is first time been caught). I know I was wr-

You didn't give a dollar amount of the items that you are accused of stealing, however since it was in a grocery store I will assume it was under $150.  Under Illinois law this would be considered "petty theft", a Class A misdemeanor which is punishable by up to 1 year in jail and/or a fine of up to $2,500.  

A first time offender is always going to be treated more lightly than someone who is a repeat offender, whether it is petty theft or not.  A judge is more likely to give the maximum penalty to someone who didn't learn his or her lesson the first time.

For a petty theft first offense you will be eligible for something known as "diversion" or a "deferred judgment".  A diversion or deferred judgment program will require that you to plead guilty to the charges however the charges will then be dropped subject to successful completion of probation.  This will enable you to keep the charge of petty theft off your permanent record.  The terms of your probation will stipulate that you do not commit another crime during the probationary period.  Additionally, as part of your probation you will have to make restitution to the store that you stole from, pay any court imposed fines, and quite possibly have to attend some type of counseling class.

Note:  If you break your any term of your probation, since you already entered a guilty plea, the charges will be reinstated and you will have to serve out the full sentence that you would have otherwise been given.

What you need to do now is to speak with attorney .  They'll advise you best on how to try and get alternative sentencing.  If money is an issue try the public defender or legal aid. 

Finally, except for consulting with your lawyer, if you did this before but didn't get caught - keep your mouth shut.  Don't lie but unless specifically asked, don't volunteer any information.