If you are talking about a single order(first order) transfer function with no zeros and one poles, then the time constant is the value where the output reaches to its 63% of its final value. For instance if the final value is 1, the time constant can be found where the output is 0.63. The other way to find the time constant is as follows:
Consider a first order transfer function as
G(s)=K/a*s+1
If the transfer function has this shape, where the s^0 term in the denominator is 1, then the time constant is equal to a. You can both try these ways in order to verify the results.
There is no tool in Simulink that automatically gives the time constant to you. You have to derive it yourself.
Secondly, to find the steady state error, you can do it as follows:
Imagine you have the same transfer function as above and you are asked to calculate it by hand. Then, in closed loop with a unit gain controller, the expression for the error will be
E(s)=R(s)/1+G(s)
Then, you can calculate steady state error(ess) by
lim s*E(s) = s*s+2/(s*s+3) where the s will cancel each other and when s=0, the ess will be 2/3.
s->0
Also in closed loop, we know that
T(s)=G(s)/1+G(s)
and the final value for the step response will be 1/3. So the steady state can be also found by
1-1/3=2/3.
Hope this helps.
