Chair Exercising

So, I'm getting serious about my health again. I want to lose 20-30 pounds but I am incredibly out of shape.
I youtubed Chair Exercises and I found a couple I like. I'll look for more.

Seated Abs Workout: Chair Exercises for Your Core - YouTube

Chiseled Chair Challenge - Lose Weight Fast with this Full Body Workout - YouTube

I couldn't do all the repetitions of the second video and I quit at the 5th minute. I am VERY sore this morning.

My question is: Do I exercise those same muscles even though (today) I can barely use them lol Or do I switch to something else and let the muscles recover.
My son says you work through the pain and that's how you build muscle. But I told him over-working them will hinder your progress.
Who's right?

I figured I'd start this thread for those of us who want to work out but are too out of shape to jump into hardcore stuff.

Post any workouts you enjoy and think will be helpful for beginners.

**EDIT**
I actually found http://www.stewsmith.com/45dayplan.pdf before searching youtube. It seems very useful.

Most athletes take a day (or two) to rest muscle group(s) that they worked on. To maximize their progress, they alternate days for which muscle group(s) they work on. For instance, you could work on core muscles on Monday, Wednesday, and Friday; and work on cardio on Tuesday, Thursday, and Saturday; leaving Sunday as a free day. This would allow core muscles to have a day to rest (and rebuild into stronger muscles) on T, R, S, and S, while cardio would do the same for M, W, F, and S.