Need help in econometric !

Dear all freinds,
Hello,

First of all, i hope that you all and your families are doing well with all what is happening now with this COVID-19. Hopping that all will be better soon.

For my study, i need to use an econometric model, actually im examining a panel data. I want to use panel least squares. I read about least squares and saw few videos, but still dont have a clear idea about all the steps that i must do before starting estimating, i know that for estimation :

1. Set the data
2. Identify dependent variable and independent variables
3. Specify the equation command in the software
4. Run the software to do the estimation
5. Get the results
6. Check the diagnostics to Confirm there is no problem with results.
7. Solve problems if any.
8. Extract results and tabulate for analysis

But before all that,

- How to determine the regression equation ?
- How can i know wich model should i use : fixed effet or random ?
- I read that we must do some tests but which tests !?

I would appreciate if anyone can share step by step instructions if possible. Im new to econometrics, so please apologise my number of questions.

Thank you in advance for any feedback.