please check out the forum rules, your question is off-topic as it is too basic for this forum.
But since stack-exchange is for getting answers, here are some hints based on my understanding of your question:
- you are looking for a beta, i.e. a regression coefficient that "describes" the relation between your chosen "risk-factor" and Netflix' returns
- you could do that by running a linear regression which has the returns as the dependent variable (y) and your chosen explaining variables (=independent variables) on the right side (x in the simple regression below) as follows:
$y=a+bx+ϵ$ (simple linear regression with one independent variable)
Your estimate of b (= beta, or regression coefficient for IV x) is then:
$b=Cov(y,x)/Var(x)$ (note that this is an estimate and might not be the true parameter).
What can you do to solve your task?
- first, have a look at regression techniques, specifically start with linear regressions
- Activate the "Data Analysis" Add-on in Excel
- get data for the returns and all independent variables that you want to include and copy them into an Excel sheet (e.g. from yahoo finance; be careful to match the daily/weekly/monthly/yearly returns to the according values of your independent variables)
- go to Data, Data Analysis and input the Data from your sheet under "Linear Regression"
- run a linear regression, Excel will give you an output with "Coefficients" which are your betas
What to keep in mind?
- be careful to include independent variables that make sense; your best starting point is to read up on the CAPM
- try to understand what you are doing when you estimate such a regression
- a linear regression might not be the best fit, i.e. might not be the best function to represent your data
- there are way better tools for this than Excel