I (US citizen) worked in Colombia the past 9 yrs. I ignorantly didn't file taxes in US while away. What are steps to begin filing past years? Which product do I use?

I filed my Colombian taxes every year but did not file US taxes. Now that I have returned, I want to take care of this. My yearly filings were straightforward -- no investments of any sort. What do I need to begin the process? What are the first steps? Can I do it myself or should I hire an expert? Any guidance will be of great help.