Nishant,
I would suggest that instead of using the single activity course, you select the topics format by selecting that in the edit settings in the course format section. You can choose to show only as many topics as you want. If you choose to show only zero topics, only the top topic section of the course will show and look similar to the single activity course if that is really what you want. You can then add as many lesson activities as you want to the course, either in that topic or any number of topic areas that you want to use. There are also, books, assignments, forums, file links, URL links, and many other activities and resources that you can create for your students. You might want to explore some of the courses in the demo site at http://school.demo.moodle.net/ to see how some of the courses are organized.
Usually activities are organized so that students can just go down the list and complete each in order. If you need something different, there are some other ways to set up links, etc. that are quite creative.
I hope that helps.