Rod Girle  Modal Logics and Philosophy Chapter 2
You can make a reasonable start here by thinking about how truth tables might work once there are the modal operators, necessary □ and possible ◊.
To remind ourselves, ordinary truth tables are filled out as follows. [What we are doing here is taking a random ordinary propositional formula, say ~A⊃B then valuing the atomic propositions in it to get, perhaps, ~True⊃False which is abbreviated ~T⊃F and then you are being asked to fill out the values for the connectives, in this case you will get FTTF.]
Truth Table Applet [Single Line]
Modal 'Truth Table Applet' [Single Line]