Correspondence is adult higher education. First of all, you should know that this is a second degree, not a full-time school. The way to learn is to take free classes by yourself, which is basically self-study. The entrance examination must be politics, English and mathematics. If you are not a native of Tai 'an, there is probably a correspondence station there, and it is not difficult to take the joint entrance examination. There are not many classes in the correspondence station (it seems that there are only a few days in a year, you can consult the school for details). You take the exam twice a year and graduate in three years. Basically, it's not too much trouble, just pay the tuition. Correspondence is mostly used for job promotion or textual research. I wish you success!