Was gibt es Nützliches oder Interessantes im Magazin? - is a question because the sentence begins with "Was" (what). Es gibt was Nützliches oder Interessantes im Magazin. - is a statement and not a question. "Es gibt" means roughly "There is" in English. "Gibt es was Nützliches oder Interessantes im Magazin? - is always question. "Gibt es" is roughly "Is there?" The reason why "Nützliches" and "Interessantes" are capitalized is because in this case they are nouns - but mean exactly what you thought. Nouns in German are always capitalized.

Rules: - In a main clause, the verb is in second position. Es GIBT etwas Nützliches im Magazin. = There IS something useful in the magazine. The subject does not have to be in first position (as it is required in English): Etwas Nützliches GIBT es im Magazin. Im Magazin GIBT es etwas Nützliches. - For a question, the verb is in first position, but after the "question word" (interrogative pronoun), which can be considered to be in "zeroeth" position. GIBT es etwas Nützliches im Magazin? = IS there something useful in the magazine? WAS GIBT es Nützliches im Magazin? = (no direct equivalent) WASfür nützliche Dinge GIBT es im Magazin? = WHAT kind of useful things ARE there in the magazine? WELCHE nützlichen Informationen GIBT es im Magazin? = WHAT useful information IS there in the magazine? So "Is there anything ...?" denotes a question, while "Es gibt (et)was ..." denotes a statement, and don't have the same meaning.