Summarize the following:
The sides of a triangle are traditionally marked with three consecutive letters, usually A, B and C. The order that you choose to mark the sides generally does not matter, unless something in the problem you are working on specifies it. Mark the three angles of the triangle with letters that correspond to the side lengths. For example, if you use capital letters A, B and C for the sides, then mark the angles with lower case letters a, b and c. You can also use lower case Greek letters α,β,and γ{\displaystyle \alpha ,\beta ,{\text{and }}\gamma }. Place these so they correspond with the labeled sides, so angle α{\displaystyle \alpha } is opposite side A, angle β{\displaystyle \beta } is opposite side B, and angle γ{\displaystyle \gamma } is opposite side C.  One way to determine that a side is “opposite” a chosen angle is to make sure that it does not form one of the rays of the angle. If labeled correctly, angle α{\displaystyle \alpha } wll be formed by the two sides B and C. It will therefore be “opposite” side A. Similarly, angle β{\displaystyle \beta } is formed by sides A and C and is opposite side B. Angle γ{\displaystyle \gamma } is formed by sides A and B and is opposite side C. Some math texts will use capital letters for the sides and lower case for the angles. Others do the opposite. It does not matter, as long as you are consistent. In your problem, you must be given some side and angle measurements. You should mark these on your sketch of the triangle. You may be able to calculate one or more measurements using some rules of geometry.  For example, if you are told that the triangle is isosceles, then you are able to mark that two of the angles are equal, as well as the two corresponding sides. As another example, if you are told that two angles are 40 and 75 degrees, you can then calculate the third angle to be 65 degrees, since all three angles must add up to 180 degrees.

Summary:
Mark the sides. Mark the angles. Label any measurements that you know.