If you keep your eyes open for a few weeks prior to a new season beginning, Showtime frequently reruns the previous seasons in blocks over a few day period, presumably to allow people to catch up.
And I don’t know which cable/satellite service you have, but if it’s one which offers On Demand as part of their services, you can usually find all the previous episodes there.
I began watching it from the beginning when it debuted but bailed about midway through the first season.
But from what I recall, it was fairly densely plotted and populated with characters and their relatiinships which it would be difficult to just pick up too far in without knowing their background storylines.
But that’s just my overall impression. Others might have a different experience.
Hopefully your service gives you a way to catch up. Showtime is generally pretty good about that.