As someone who doesn't travel and doesn't intend to travel and doesn't care about miles, I found the travelmiles101 course to be not particularly relevant.
There used to be ways to manufacture spend to fairly easily reach the minimum spend required for some bonuses...I did a tad bit of this last year, but then the easy options dried up. I'm not willing to go to the risk or effort that manufacture spend currently requires.
I'm interested in cash. And I want it to be easy, I'm not going to jump through a lot of hoops. My favorite cards are Chase cards because you can deposit your 'points' directly into your bank account as a cash deposit or do a statement credit. The Chase Sapphire preferred is the first card that I got (inspired by the MMM article). I think it requires a $4000 spend within the first 3 months to reach the bonus - but that's a nice cash bonus!
If you just want to get your toes wet without the stress of trying to reach $4000 minimum spend you can apply for the Chase AARP card. (Google it, I don't want to post links). I got this once for myself and once for my husband. We are both in our early 30s so you don't have to actually have any relationship with the AARP. The AARP bonus is $100 after spending $500. That's a very easy one. I closed the cards after we got the bonuses. There are quite a few other $100 for $500 cards around as well, the AARP one is just the one I remembered first.
I find cards by keeping an eye out on forums for discussions over credit card bonuses or by googling for best credit card offers. Sometimes there are offers mentioned in the TravelMiles Facebook group (so I don't regret taking the course, I just didn't feel like I learned anything that helped my specific situation).
You asked how to determine what you can redeem points for (this is a great thing to figure out BEFORE you apply for a card!) Again, I google it. I scroll through the google results looking for something that isn't related to the company. So I just googled 'Southwest Points' and the first result I bothered clicking on was an article from NerdWallet, the second was an article from ThePointsGuy (both of these sites I've used before). Unfortunately neither result mentioned spending points on anything other than miles, so then I googled 'Southwest Points for Gift Cards' and found
https://www.southwest.com/rapidrewards/redeem-more-rewards. So it looks like you can turn southwest points into gift cards <for example a $25 Target Gift card costs 3,000 points>. But I certainly wouldn't start with a southwest card if all you want is cash.
If you don't want to get into churning, there are still quite a few nice and easy cash back rewards credit cards that you can get and just use for your daily spend. My two staples are the Sallie Mae Rewards Mastercard from Barclaycard which I keep because I get 5% cash back on Amazon all the time. I also have a CitiCard Double Cash back which essentially is 2% everywhere (be sure to choose direct deposit into your checking account for the cash back versus a statement credit because statement credits on this particular card reduce your cash awards).
It's all quite overwhelming at first. Just pick a card that has a sign on bonus that you can meet. See how it goes. It gets easier after you've done it a few times.