If entity walks on block...

I know there are a few other people on this topic, but they're all asking for help with their versions of testing if an entity walks on a certain block, I want help uh- coding that (I don't know how to code in Mcreator don't judge). I'm trying to make it so that if an entity walks on my custom block, particles are emitted from the top; I can't find anyway to detect if the player is standing on it. Please help, thanks! :D