Apply effect to all player when they enter the game, 1.16.5

Hi Everyone, I'm very new in modding. I started following a few tutorials, creating special item and special blocks. After two weeks of hard searching i could't find out how to create these two feature : 

1) I would like to apply an effect, like fire effect to all player.

2) This effect change according to the player position (at open air or in his house)

Do you have any tutorial or guide? 

Also the other things that I would like to do is to create a custom effect. This custom effect start from nausea and after some time will become to burn the player. 

Thank you