That's a very general question. It depends of what you were using Flash (Player) for. Are you ..
a game creator?
an instructional designer (eLearning scenarios)?
a web author?
a 'rich internet applications' developer?
maybe something else entirely or everything rolled into one?
I've read your post here, and it sounds to me that you used Flash (Player) to publish videos (on websites?). If that's the case, be aware that HTML5 includes since 10 years a video element. Find relevant infos on w3schools.
For all other opportunities what you want to do ..
if you are into game creating, search for Unity or ITyStudio.
if you are an animator, look into Adobe Animate. Be here aware that this is the predecessor of the former Flash Pro authoring tool. And with the integrated API CreateJS for publishing for HTML5 you can create quite advanced interactive contents.
if you are into eLearning, consider Adobe Captivate or Articulate 360.
These are a few avenues to replace the Flash Player. Don't get stuck on the 'old' ways. It is high time to start looking for alternatives and master a few learning curves.