Can chemotherapy control the cancer? What is the goal of each treatment?

Ask your doctor! That is a great question and a really important one to ask your doctor! the goals of chemo are different for each patient and each cancer type. Sometimes the goal is to completely cure the cancer; sometimes it is to prolong life but not cure the cancer. Sometimes the goal is to relieve symptoms. It might be a hard question to ask, but you should know your doctor's goals for you!
Shrink it too. In addition to what dr. Webster has listed, sometimes chemo is used to shrink the tumor so that it can be surgically removed. It i'd a great question to discuss with your cancer doctor.
Chemotherapy. Yes, chemo is used to control cancer. Generally speaking- the goal can be divided into 2 : curative intent ( given after definitive treatment-like surgery or before surgery with the aim to shrink the tumor so surgery can be carried out ) or - to relieve symptoms. The goal will depend on the stage of cancer, how good your condition is overall , other diseases etc. Please discuss with your oncologis.
Tough question. Chemo is certainly help a lot of colon cancer, with all 5 chemo we have now, people can live upto 36 months, without them, only 6 months to 12 months. However, we do not cure most advanced colon, and in my own lab and others research too, chemo created a lot of cancer stem cells, shocking fact, so we are trying to understand this better and figure out how to reverse this process.