What is a double column format newspaper article?

It can be one of two things. The first is a structural thing: the newspaper is laid out in narrow "strips" of type, and each of those strips is called a column. The other is editorial: if someone writes a regular article on a particular thing, those articles are called columns. Probably, although I'm not exactly certain, because the writers were given one full column's worth of space (which would be around 20 inches long, in most newspapers) in the paper. I assume you are asking because you read that Eleanor Roosevelt had her own column, and that is what this means: she wrote regularly, and her opinion pieces and commentaries were syndicated to a number of newspapers.