How to generate multiple-criterias to find a WebElement

I am new at testing so my apologies in advance if my question sounds a bit primary.

I use Selenium and Java to write atest, I need to find and element by more than one criteria.

I saw this question on stackover which is exactly what I mean, but the answers do not work for me as I do not know what is //input[(@id='id_Start') and (@class = 'blabla')] and how to generate it.