how i can link unity to my database and let users access their accounts on a login on the game

Hello guys first thanks for seeing this and trying to help me

i want to start a multiplayer online browser unity game and here is the idea of it :

i have created a website for the game i have created the database and the signup and login and now iam trying to create the game :

when the player signup i want him/her to pick a character which he will use to play all the time on the game (when he login again he use the character that he picked)

players can play vs others on the game and can talk with others on a chat which can be (public) (private)...

so guys how i can :

create multiplayer game that users can login into the game and play vs others.

also i would like to add that the player have a ranks which start from rank0 and when he play game he get experience which move up his rank and the player also got gold coins and those stuff and he can send gold to other player and so on