Selecting data from a mapping table using a foreign key
It is the same
SELECT gl.Title, gl.Genre, gl.Plattform, gl.ReleaseDate, gl.Price
FROM GameList gl
INNER JOIN UserGame ug ON gl.GL_ID = ug.GL_ID
WHERE ug.USR_ID = 10;

As long you have the User_id you don't need more, but if you also want information from the users table
SELECT gl.Title, gl.Genre, gl.Plattform, gl.ReleaseDate, gl.Price
FROM GameList gl
INNER JOIN UserGame ug ON gl.GL_ID = ug.GL_ID
INNER JOIN Users u ON ug.USR_ID=u.USR_ID
WHERE ug.USR_ID = 10;