Is just working out enough for the muscle to grow? No of course.
You need proper rest and proper supply of nutrients in order to grow.
Usually natural bodybuilding takes time and sometimes it can be tough to actually see the muscle growth itself.
  Lets look at this in simple way.
Working out stresses your muscles.
After that they need to reform again stronger than before.
The fastest recovery is happening while you are at sleep.
At this time the nutrients you took from your food come into action.
There are several 'symptoms' that your body indicates that is building the muscle.
Strength increase - this is the simplest indicator.
As you feel the weight is getting lighter workout after workout - you are getting stronger.
This is indicator that the muscle is growing.
Keep the progress and don't get lazy.
Keep in mind if you haven't worked out for a month you might have reserve strength.
You may be able to lift more heavy than the regular for workout or two.
Less urinating - this is again indicator of muscle growth.
The recovery process of your body requires more fluid.
This usually means that you will also get more thirsty.
Keep a bottle of water near you.
Keep yourself supplied with fluids.
Water is the most recommended.
Keep in mind getting thirsty does not always mean your muscles are growing.
Anyway no matter the case don't let yourself dehydrated.
If you don't feel thirst naturally that common, just keep some water near and drink a little from time to time.
Your skin feels tight.
This is due the muscle growing and pushing the skin.
Usually it is only detected by muscles that are easily 'pumped'.
Your skin will adapt very quickly and the sensation will be gone.
Keep in mind unnatural fast muscle growth may deliver skin stretch marks.
Muscle Spasms - sometimes your muscle will contract very slightly in rapid manner without your control or intention.
This is often felt during rest times.
Sometimes can be little weird but keep in mind it is the process of growing.
Don't be worried.
This often happens in the shoulder, the biceps and the other muscles that are not typically used in the everyday life.
What some call the secret of building muscle is to keep track of those symptoms.
When there are few present the idea is to eat properly and rest actively.
This is when your body needs rest and nutrients.
Some even say it is actually bad idea to go to the gym at this time.
Although there is certain sense behind this call I will not only rely on that.
Some people almost always have such symptoms and this will probably mean that they must work out once in a week.