how do i earn money through blogging?

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i have my own blog and i learned that i could write articles and post it on my blog in order to earn money. however, i am not sure how it works, i get approval from some blogging sites where i have to bid. that's the part i get confused with. do i write the article and post it on my blog first, or do i have to bid and wait for a sign or something before i actually write anything? help!