The "into" and "in" should be explaining it to you , I ll try to put it another way to possibly make it clearer for you : The Akkusativ will be used when there is a movement from one point to another in the action of the verb before "in". While the Dativ will be used when there is no movement ( but possible in place ) but no movement from one point to the other ) in die Tasse giessen --hier Akkusativ weil Tee wird gegossen and there is a movement from a point to another in the action of "giessen". in dem Haus bleiben ,, hier Dative weil es keine Bewegung gibt ( of course man bewegt sich im Haus , but the "bleiben" action is not a moving action . Ins Bett gehen ,,, Akkusativ , you are not in bed and you are moving from a spot to the bed to sleep in it , so there is a movement towards the bed ). im Bett liegen .. hier Dativ ( no movement ,already in bed lying ) Another good example : in die Strasse gehen in der Strasse gehen Here you have the same sentence but it is once in the dativ once in akkusativ , thus giving two different meanings. in die Strasse gehen bedeutet du bist in der Strasse "x" and gehst in die Strasse "y" , you are moving from a point to another , , movement so Akkusativ . in der Strasse gehen bedeutet du bist in der Strasse "x" und gehst innerhalb der selben Strasse ) ( so the verb hier doesnt indicate moving from a point to another but inside the same place ) . I hope this is a bit clear for you :)

Oh sorry your base language is English. Just noticed...ahahahahahaha in + Akkustaive = IN(TO) in die Tasse = in(to) the cup; ins Bett = in(to) bed in + Dativ = in, within in dem Haus = inside the house Thas should clear it all up!

in + Akkusativ = 到——之内 in + Dative = 在——之内