第一句是一个复合句,If引导的是一个条件状语从句,people那个是主句,主从句不是并列关系,所以不能加and,起连接作用的词是if.
第二句中and连接的是两个并列句,前面可以加逗号.
and做并列连词时,它前后连接两个相同的语法成分,如动词,名词,形容词,甚至是句子.
如：i'll go to school and study hard.
i will call on a friend,and we'll go to museum together.
通常来说,“and"前后连接两个相同功能的词时,前面不加逗号；而连接两个独立的句子时,前面有逗号隔开.
They can also send emails at any time,and get the latest information through the Interent,which is open to both teachers and students in school.
另外,and在连接两个不定式的时候,后一个不定式要省略to
如：we'll intend to go home together and play CS.
这是固定的语法习惯.