On the question of where to start if you have never done a serious exercise routine, Mark Rippetoe's starting strength (Taser posted a link above) is what I did in college when I started lifting. I did gym class in grade school and went hiking with my family, but I was never on a sports team, never got into biking or skateboarding, etc. I was nerd with no gym experience. Practice form with an empty bar until you feel like everything is perfect (it isn't, but it will feel like you nailed everything). Don't start with weights too heavy, you can always move up next week. And you will move up FAST. You don't need to memorize a ton of different lifts, just do a couple and do them right. Once you have the hang of it, your gym sessions will be really short. The lifts you are doing work multiple muscle groups, so you are essentially doing the work of 5-8 sets on isolation machines all at once.
Give it a few weeks to become a regular rhythm. Once you can do it all with your brain turned off, start tweaking your routine. What parts of your body feel weaker, or like they're behind what the rest of your body can do? Add some isolation exercises (machine or freeweight) to help them catch up. By this point you should have a basic understanding of gym shit, and a basic level of fitness. Go hog wild! Try variations on the lifts you already do. Try something new. I found out that I really like doing rows (no particular reason, I just like them). I got into all the goofy variations on them for a while and loved it. At this point I was finally able to do chinups and pullups, which I had never been able to do my whole life. The majority of people you know probably can't even do a single one with good form. Well, here in America at least. That gave me motivation to keep at it.
Get a kid, eat proteins, give sugar to him, carry him around everywhere and do all kinds of shenanigans.
I'm just kidding, your back will be in severe pain if you do as advised 
Witchcraft Jr. is kind of a picky eater and I don't just let him have chicken tendies or pizza when he won't eat his Actual Dinner, so he is a little on the slim side. Lil fucker is tall though, so he's still 50 lbs or so. Lift a Kid is good exercise and they think it's the funnest thing ever.
