It would be helpful to give a brief overview of what will be covered in each lesson at the top of the page. This could either be a bulleted list of the topics, with an introduction saying "This lesson will cover: ...". Or a brief text description. For lesson 3, this text description could be something like: "This lesson provides an introduction of how to work with data frames. We will cover how to examine the contents of a data frame, how to refer to particular components, and how to subset data frames based on position in the data frame or based on logical operators. We will also look at how to sort data frames and how to combine them."
Alternatively, for Lesson 3, you could say: "This lesson provides an introduction of how to work with data frames and has sections on:
It would be helpful to give a brief overview of what will be covered in each lesson at the top of the page. This could either be a bulleted list of the topics, with an introduction saying "This lesson will cover: ...". Or a brief text description. For lesson 3, this text description could be something like: "This lesson provides an introduction of how to work with data frames. We will cover how to examine the contents of a data frame, how to refer to particular components, and how to subset data frames based on position in the data frame or based on logical operators. We will also look at how to sort data frames and how to combine them."
Alternatively, for Lesson 3, you could say: "This lesson provides an introduction of how to work with data frames and has sections on: