It's relatively easy to get to Port Chester by car. There are Port Chester exits off of I-95, 287 and the Merritt parkway. Driving around Port Chester gives you the option of seeing some neighborhoods and areas that you'd miss if you took a bus, train or tried walking.
Port Chester is a very walkable town. The main thoroughfare through town is Westchester Avenue and the post road/main street. Although mild hills are everywhere nothing will be more than a 10 minute walk.
We try to get out and walk as often as possible when going to the local restaurants or the movies or even shopping if we aren't buying a lot. Of course as is good advice while driving, we often combine all of the above in our walks at the same time too.
Metro North's New Haven line runs through and stops in Port Chester. Approximate running time from here to Grand Central is 37 minutes on the Express which runs from NYC-Rye express and then Port Chester is the next stop or 47-50 minutes on the local.
Current fares to the city are $9.50 peak and $6.75 off peak.
The Bee Line bus system of Westchester County serves Port Chester. The bus I use is the 13. It will take me to work on days I don't feel like working and also across county when I need to get to the Tarrytown Metro North Hudson line.