How to properly create composite primary keys - MYSQL

I would not make the primary key of the "info" table a composite of the two values from other tables.

Others can articulate the reasons better, but it feels wrong to have a column that is really made up of two pieces of information. What if you want to sort on the ID from the second table for some reason? What if you want to count the number of times a value from either table is present?

I would always keep these as two distinct columns. You could use a two-column primay key in mysql ...PRIMARY KEY(id_a, id_b)... but I prefer using a two-column unique index, and having an auto-increment primary key field.

I would use a composite (multi-column) key.

CREATE TABLE INFO (
    t1ID INT,
    t2ID INT,
    PRIMARY KEY (t1ID, t2ID)
) 

This way you can have t1ID and t2ID as foreign keys pointing to their respective tables as well.