First you need a hacked switch to extract and inject saves on the switch.
If you dont want/dont have a modded switch , use a bot to send the pokemons to your game.
Next, if you want to use pokemon online with a modded switch, you must have a legal copy of the game.
If you have that, then pkhex its the easiest part
A) download a save and inject it on your profile
B) download a save, extract the pokemons as pkX files and inject them to your save
C) create the pokemon manually and inject it to your save
D) donload the pk files and inject them to your save
In regard of how to use pkhex, i reccomend first check some youtube guides, read guides, or whatever you want, and then aks specifically what you dont understand