As David M. says, it is a matter of style.
In British English, we now generally use the same convention for titles as for plain text - nothing is capitalised apart from the first word and proper nouns.
American English is more traditional, as it still capitalises all the meaningful words in titles. Non-meaningful words (articles, prepositions and so on) are not usually capitalised. However, as David says, you do sometimes comes across titles where all the words have initial capitals.
I don't think it matters too much.