Creating a new variable from likert scale questions

Hi everyone,

I conducted a survey for an assignment in my research lecture. I am examining the relationship between "mobile device usage" and "academic success". Here is my variables list:

Independent Variables:
- Attendance
- Tiredness
- Mobile Device Usage

Dependent Variable:
- Academic Success

I prepared my questionnaire consist of 25 questions. Here is the live form:
I collected the answers and transferred them into SPSS. I also completed to give labels for each value.

At this stage, I do not know what exactly had to do.
I have more than one questions for each variable. How can I prepare only one variable that reflects my research topic variables(for each)?
Am I compute the results or average them?

My lecturer expect us to design a linear regression model.
If necessary I can share the spss file.

Any reply would be greatly appreciated.