How do I decide which AdWords networks to activate for my account? And how can I determine whether the Search and Content networks are generating returns?

AdWords gives you the option to display your ads in three places:

1) The Google Network: the search engine results pages (SERPs) of Google.com.

2) The Search Network: the SERPs of affiliated search engines such as AOL.com.

3) The Content Network: the advertising sections of affiliated sites such as blogs and newsletters.

All campaigns need to include the Google network, but otherwise you can mix and match somewhat. I would suggest that you run one campaign using the Google and Search networks, and, if you're interested to see if the Search network generates returns for you, another campaign using only the Google network. If your ROAS or CPA is significantly better on the Google-only campaign, you're probably being hindered by the Search Network. You should also run Content campaigns separately for a similar test. Given the fact that Content campaigns tend to provide low-cost impressions but low conversions as well, you'll probably want to minimize your spend on those campaigns.