Perhaps you've been away from the Church for a while. Maybe a LONG while. To Our Lord, it doesn't matter. There is much rejoicing in Heaven that you are thinking about coming back.
The first, and easiest, step is to find your closest parish and talk to the priest in residence. They can walk you though all the process. For some, it may be as simple as going to Confession. For others, there may be life-long hurts that need to be healed. Questions that need to be answered. Either way, your local parish is there to help.
Search for your closest parish HERE.
You can also get some information from Catholics Come Home