The Karnaugh map (KM or K-map) is a method of simplifying Boolean algebra expressions.

For me, I don't think karnaugh map is very important at all. (just think about any one of modern programming language, and you will know what I'm feeling)

So I just want to give a picture with a few words. (Chinese book may not the same with what I show you, it's OK, you have to know China usually don't follow the International Standard, it may because of 知识分子素质太差，一叶樟木，井低观天)

Here if we set $1$ as $A$, then $0$ is $\overline{A}$

Here if we set $1$ as $B$, then $0$ is $\overline{B}$

Here $CD$ or $AB$ both connected to the line besides it.

So you can represent $m7$ as $\overline{A}BCD(01 11)$，$m13$ as $AB\overline{C}D(1101)$

Google for more information. or if you know Chinese very well, see following.

1. 翻出你的教材对照着看
2. 该表是个球体，x与y是相连的
3. 为了最简，同一个方格最好只被圈一次
4. 0、1同时出现在一竖或一横，消去；一横或一竖出现相同的0或1，保留
5. 先读AB, 竖着；再读CD，横着（反正随你的图而变）
6. 田字四格化简程度大于两个相邻格

update

1. 翻出你的教材对照着看
2. 该表是个“救生圈”，x与y是相连的，四个角也是相连的(可以连成一个田字格)
3. 8 > 4 > 2，这里的数字指的是每个圈所圈住的相邻项的个数，尽可能用大圈
4. 为了最简，圈的次数尽量要少
5. 0、1同时出现在一竖或一横，消去；一横或一竖出现相同的0或1，保留
6. 先读AB, 竖着；再读CD，横着（反正随你的图而变）