Yes, step in I guess. I never actually got it completely on my dog who looks a lot like the picture. It did not seem to be adjustable in the right places. The arm holes were too big and overall the whole thing was too big although I selected then size that matched his measurements. If you try it maybe order a size down in addition to see which might fit better. Also it did not work with the type of collar we use. Overall it was just too "fiddlely" and life's too short.
The dog has to put the left leg through a large opening. The plastic fastener (type typically used on many collars) is on the right side. My largest dog (~62 lbs) and my smallest dog (~30 lbs and 15 years old) wear these coats and I have no problem getting them on them.