lets say assume that we have Xt=0.5+0.25t-1 and and the mean reversion is 0.666
does the 0.666 mean that on the long run, the mean of the above equation will be 0.666?
I presume that you mean:
X_t_ = 0.5 + 0.25X_t_-1
To see how it behaves, you should either bang out a dozen or so iterations on your calculator, or try it in Excel.
You’ll get a lot more out of this if you do it yourself rather than asking someone for the answer