Modrinth help (new user)

(Not a native speaker, sorry): as the title says, I’m new to mods as I’ve only played Minecraft on console before. No I’ve got a new PC, bought Minecraft and sainted to play with some mods. Watched some videos and wanted to install Cobblemon so I downloaded modrinth. I also found some other mods I liked but I can’t find a way to use two or three mods at the same time. I can run mods individually via modrinth by clicking on play, but I don’t know what to do next. I’ve tried do find help online but only found old threads that didn’t provide any help.

And I’ve got another question: can I play the mods from my normal Minecraft game that I’ve bought? It seems that when I open mods via modrinth, it start its own version of Java. I can’t access mods from my „official“/„normal“ Minecraft Java version.