The following answers apply to the transcendental RootOf. The situation for the polynomial RootOf is slightly different.
Q1) How can I evaluate the RootOf?
You can substitute values for the variables and apply commands to it just as you can with any other expression. Just don't substitute for the "with respect to" variable (the _Z). That wouldn't make sense, just like substituting a nonatomic expression for x in int(f(x), x) or solve(f(x), x) wouldn't make sense.
Q2) In other words, What is it saying?
A ?RootOf is Maple's way of expressing an inverse function (usually with multiple branches) for which it otherwise has no expression. Another way of thinking about it is that it's Maple's way of expressing an implicitly defined function (usually one with multiple branches).
Q3) Is there any way that I can get an expression without RootOf for the variable that I am solving for?
For an exact symbolic solution, generally, no, not unless you are aware of some solving technique which Maple is not using. A floating-point solution is usually possible if you supply numeric values to the parameters. In either case, you can try to apply the command ?allvalues. That is the command specifically designed for expressions containing RootOf. Especially, try to reduce the RootOf expression with allvalues if you have assigned numeric values to some of the parameters. If you've applied assumptions to some of the parameters, then try simplify.
Q4) Is there any way that I can get an analytical expression for the variable that I am solving for?
I am guessing that what you really meant by this question is what I answered in Q3 above. But I separated out this question so that I coud point out that an expression with RootOf is an analytic expression. You can generally apply to it all the Maple commands that you would apply to any other analytic expression, including diff, series, simplify.
Q5) Or from here we can only get numerical means to solve for the variable. If so, how to proceed?
Use ?eval to supply numeric values to the parameters, then apply allvalues. At this point, you may need to select a branch. Then apply evalf. There are cases where not all branches will satisfy the original equation, so plug back into the original to check.