Making a k-map from an equation
1. The first step is to express the SOP in its canonical form. 

It means that each term in the SOP must be the product of four variables. 
In order to make so, multiply (AND) each term with (m+m') where m is the missing variable. If more than one variables (m, n, o ...) are absent in the term, then multiply with (m+m')(n+n')(o+o') ....

Considering your example, w'x'y' + wx'y'z', the first term is missing z in it. So multiply by (z+z').

w'x'y' + wx'y'z' = w'x'y'(z'+z) + wx'y'z' = w'x'y'z' + w'x'y'z + wx'y'z'

2. Then put 1 in the K-map cells corresponding to these minterms. ie., (0,1,8).

Similarly, logical expressions in POS can be converted into canonical form and filling corresponding maxterms in K-map with '0' will also give you the result.