What is the main config file here for Yii2?
main-local.php
main.php
params-local.php
params.php
Do I have to keep all these?
In the contents I see:
$config
$params
They both look about the same in format, I don’t know when adding something where to put it in.
Please be kind, I am just learning.
Are you on the advanced app template? In any case, see here. This can be confusing at first, but it gets better in time and you will soon see the merits of this. I promise 
Rule of thumb: Everything ending in [font=“Courier New”]-local.php[/font] should not end up in version control as it is supposed to override the defaults set in the other files with values that are correct on your system only.