The formal-form ("desu"-table) using if you e.g. with teacher or with another higher person speaking...
And the daily-form ( "da"-table) using if you with your family or with friends (how I)...etc. speaking...
E.g.: I'm would your teacher be, then would you to me say: "O-hayou degozaimasu x-sensei! (Good morning x-teacher!) Kyou wa ii tenki desu ne~ (Today is a nice weather~)". And I if your firend would (but we are), Then so: "Kimi ga ii da (You're nice...)...etc."
I find that the best way to learn kanji is to get some Japanese reading material and have a dictionary beside you as you go. It's painfully slow but it gets absorbed.