If you have to ask questions like the original one then you need to worry about other things...
Seriously.
Not exactly. It's normal for any newbie to wonder whether it's worth his/her while to get into the industry.
Here's a course for you since I'm feeling nice:
1. If you have capital, great. If not, work toward getting around $5-10k before considering moving forward. Otherwise, you'll gain little experience, data and waste your time.
2. Decide whether you want to work mobile or not. I'd recommend working off of mobile when you're more experienced, but many people choose to work differently.
3. Find a broad niche that you can gather interest and research for (finance, dating, gaming, etc.)
4. Pick an offer to run.
5. Find suitable traffic sources to drive traffic to your offer (research what kind of ad networks offer quality traffic with volume availability)
6. Build ads that you can track on your backend. And if there's data that you can't track (like age or gender), then build multiple ads and segment them by your tracking preferences (e.g.: Ad 1 = age 25-28, Ad 2 = age 29-32, etc.). The kind of data your ad network can offer to you varies across each network, so determine what you need to track individually.
7. Analyze: Find which kinds of audiences work best with your offer and optimize your ads to target only those audiences.
Expect a negative return from the beginning. Whenever I work in any kind of niche, hitting -50% ROI off the bat is great because it means I'm that much closer to breaking a profit. As you get advanced, you'll want paid intelligence tools that break down pre-existing data on various offers/niches for you; improving your campaign efforts from the very beginning.
Once you've gotten to the later stages, feel free to PM me for help on optimizing your campaigns.