For posting ads, you just head to the section you want to post an ad in: Classifieds, Housing, or Jobs. Each section has a link in both the site header and site footer. On each page, you'll find a big button in the top right corner for creating an ad.
For reviews, you just need to find the Spot you are looking to review. Hover over the "Top Spots" link in the site header and enter the name of your Spot in the search box. Once on the Spot page, you'll find a button for creating a review in the top right corner.
If you do not find the Spot you want to review, you'll find a link for creating a new Spot in the site footer or on the Top Spots page.