You should use the foam roller at least a couple of times a week. You can use it every day. It may be uncomfortable for the first couple of times using it, but it will get less uncomfortable the more you do it. You should stretch a couple of times a week also. It’s good to do these on recovery days or when your muscles are feeling tight.
This video also includes the Core workout listed in the training plans. If you only want to watch the stretching and foam roller part of the video, start the video at 6:13, about 1/2 way through.