What kind of rules help to convert an expression into a 3 input NOR expression? Do all variables have to be of the form (a+b+c)' + (d+e+f)'? What happens if there is an expression that is just (a')' that is to be made into a 3 input NOR - could you simply NOR it with itself?
More specifically I'm trying to get help in converting this equation into 3 input NOR:
H = M + CR + CD'
If you are talking about $\mathtt{NOR}(x,y,z) = \neg(x \lor y \lor z)$ then
\begin{align*} \mathtt{NOT}(x) &= \mathtt{NOR}(x,x,x) \\ \mathtt{OR}(x,y,z) &= \mathtt{NOT}(\mathtt{NOR}(x,y,z)) \\ \mathtt{OR}(x,y) &= \mathtt{OR}(x,y,y) \\ \mathtt{AND}(x,y,z) &= \mathtt{NOR}(\mathtt{NOT}(x),\mathtt{NOT}(y), \mathtt{NOT}(z)) \\ \mathtt{AND}(x,y) &= \mathtt{AND}(x,y,y) \end{align*}
Also, be aware that $(x \land y) \lor (x \land \neg y)$ is equivalent to $x \land (y \lor \neg y)$ and that simplifies to $x$.
I hope this helps ;-)