p = The forest is dark

q = The moon is full. 

Start with

       The forest is dark or the moon is full.

Replace the words "The forest is dark" by the letter p.  Then you have

                        p or the moon is full

Replace the words "the moon is full" by the letter q.  Then you have

                        p or q

Finally replace the word "or" by the symbol "⋁".  Then
we have

                        p ⋁ q

Now to make a truth table, you need the rule for disjunction ⋁

Rule for disjunction:

If the truth values of what is on both sides of ⋁ are both F, then 
⋁ has truth value F.  Otherwise, it has truth value T.

p   q   p⋁q
T   T    T
T   F    T
F   T    T
F   F    F

Edwin