1. I help my mother to do housework.

2. He helps me to learn English.

3. His parents help him to study for the exam.

4. I'd like to help mum to do some housework after school.

5. She helps her brother to carry the heavy bag.

在这些例句中，"help sb to do sth"结构用于描述帮助某人进行某项具体的活动或任务。其中，"to"是不定式，用于引导目的状语，但很多时候这个"to"是可以省略的，特别是在口语和非正式书面语中。例如，在文档中也可以看到"I help my mother do housework"这样的表达，这种省略"to"的形式也是正确的。