Follow this:
EM -> Security -> Logins -> R-Click -> NewLogin -> Database Access tab
Choose your databases that you want to grant READ ONLY access by check infront of it.
And for each databse, you have to check db_datareader at the below pane.
And you are done!
This is simple to undrestand but you can find more about it in BOL. To start, you can search sp_addlogin.
Canada DBA,