Adj. with ing.help please

so i have a problem with the verbs that are transform in adjectives....such as rocking chair ,and sleeping bag,or speaking book....i know that the first two are for use rocking chair ,for ex. is a chair that is for rocking but in spanish speakers in tends to confuse because you tend to think that the chair is rocking itself i mean the chair is rocking itself ,same thing happens if i say a watching tv for example it sounds as if the tv was the one that is watching , it's kind of difficult to explain this ,for example a speaking book sounds like a book that speaks, but the books cant talk so i can assume that is a book for speaking skills.
My question is how can i recognize and build a modifier knowing that is right ...for example if i want to say a tv that is for watching i would say a watching tv? i dont know ,but it sounds like if the tv was the one that is warching and not the one that is for watch or sleeping bag ,i know that is a bag for sleeping but it sounds like if the bag was the one that is sleeping

please help me here im so confused

thanks a lot dan