Translation:In some cases, I do not know how to use the words.
Possibilities: 1)you are learning a language and sometimes you cant make up sentences, 2) you find it difficult to speak your mind in some occasions it seems like u just cant find the words, 3) sometimes you cant figure out the grammar rules on your native language...
A truer statement has never been said.
I tried to make this sentence and it was true again! Let me know if this makes sense: Uma afirmação mais verdadeira não tem falar nunca.
nunca foi dito uma informação mais verdadeira. (you chose a hard sentence,=))