For the people that have never worked out and decided to start, they don't know what they are in for! But, I will give some indication as to what to be ready for.
The main thing one has to realize is that when you start working out after a lay off (or maybe just have never started to begin with), you use muscles in a way you probably don't do every day. When this happens, the muscles say "hey, what in the world just happened? I'm not used to doing that movement. Guess I'll have to start adapting."
Yes, you'll feel tired when you're doing with the workout, but the real "soreness" may not happen for a day or two after you do the workout. This "soreness" is commonly referred to as "DOMS", which stands for: Delayed Onset Muscle Soreness. If you've experienced this, you'll know that it's a good soreness, as I like to call it. This is what you WANT to feel after a workout.
I call it a giggly-pain soreness. It's the type of pain you laugh at, like the day after doing squats your leg muscles are sore when you try to get up from a seating position and you giggle about it. It's not the ouch-pain that's just an outright sharp pain. If you've experienced it, you'll know the difference.
Once a new person experiences this feeling, they don't like it (because it's so different) and therefore, they may feel they did something wrong with the exercise and decided to stop working out.
My advice is to NOT STOP working out! The DOMS are what you WANT to feel! Now, just so you know, one thing you do NOT want to do is STOP WORKING OUT! Oh sure, you may want to wait a couple of days to repeat that particular exercise or series of exercises, but please do NOT STOP WORKING OUT! Do something different, a totally different body part for your next workout, but keep moving forward!
Your goal, as a new workout person, is to achieve this DOMS feeling with every workout. No I'm not crazy, I'm just telling you like it is. I personally like it what I get DOMS, it tells me I'm doing something right for my body.
Once you experience it, you may not like it the first time, but once you understand that DOMS are from accomplishing something, you'll be looking forward to them!
Now, go out there and work for those DOMS!