Your blog will have to be approved according to how many subscribers and traffic you have.
Once you are in the review system, advertisers choose which blogs they want to review their product and you get notified if you are chosen. The better your rating as a blogger the more reviews you will be able to do per month.
Reviews have to be a minimum of 200 words and you will have to make it clear to readers that it is a sponsored post.
If you are not approved on your first application you can always submit your site again once your traffic has increased.
Payments are made via check with a minimum $25 payout. Payout via PayPal has no minimum.