I have seen geometry proofs described as "2 column" proofs.
Generally speaking what this means is that each line in your proof must be justified using already proved theorems or accepted axioms. In the left "column" are the statements you use in your proof and in the right "column" are your justifications.
A a good example look at the proof of "Pons Asinorum", the theorem which shows that the base angles of an isosceles triangle are equal. You will need to use axioms (when equals are subtracted from equals the results are equal) and previous proofs (SAS="Side Angle Side).
I hope this helps.
