From the looks of it, you are cutting members CD, CL, and ML and analyzing the remaining section to the left. Next, I assume you correctly calculated the reaction force (100 KN) at the pin support A. Finally, I assume you chose the directions of the unknown forces acting on members CD, CL, and ML arbitrarily as being in tension (away from the joints).
It's ok to assume the directions of the forces, but in order to determine what the directions actually are you have to calculate their actual values. You do this by (1) summing the vertical forces and setting them equal to zero, (2) summing the horizontal forces and setting to zero and (3) summing the moments of the forces about A and setting to zero. If the magnitudes of a calculated force is positive and it is pointing away from the joint, you have tension. If it is negative and pointing away from the joint you have compression.
You only have one unknown vertical force, CL. Its value and therefore direction will be obvious. You have two unknown horizontal forces, ML and CD. In order for them to sum to zero, one of them has to be chosen in the wrong direction. In other words, one of them has to be in compression. CD contributes no moment about point A, but ML and CL does. Since you now know CL, summing the moments of all the forces about A will give you ML. From there you can find CD. The signs of the results will tell you if they are in tension or compression.
Hope this helps.
When you become more familiar with statics you will in some cases be able to determine whether members are in tension or compression simply by inspection. But until you get more familiar with the subject, it is best to do the detailed calculations.