I don't understand why most of you choose the sandbox games. If you play the Scenarios (start a game) - until scenario 14, all of them are tutorials. If you fail, you can restart the scenario with easier goals, and continue enjoying the game.
Training the staff:
1) Click on the Information Center button below (hover over the buttons).
2) Click on the first upper button.
3) Click on the 3rd (not sure, may be the 2nd - hover) left button.
A window will be openned with two lines: the first one is with blue color, showing your staff training skills.
The lower line is empty.
You can click on any place on the lower line, and you'll see a yellow line, and at the bottom left of the page you will see how much money you invested in training.
Be careful not to invest too much money, because if the restaurant looses profit, it affects the staff morale.
There are many reasons why the food is cold:
If you have 2 floors openned - you need dumbwaiters. If you lack them, the servers are running from floor to floor, and it's a long way, which causes the food to become cold.
The dumbwaiter is a lift, used by the kitchen porters to deliver the food from one floor to another. It has the form of a tower. You must place it in the kitchen only, and it will be seen on the other floor.
If you have dumbwaiter - may be you have too many tables, close one to another, and the servers can't pass among them.
You have to assign your servers and captains to floors: open the staff panel, click on the name of the worker, and under his picture you'll see 3 options: 1st floor only, 2nd floor only, and auto.
For these options, you have to download the Patch from the main Enlight site, according the version you play.
In Hotel Giant (another game of Enlight/Jowood), cold food was the only sign that the kitchen is far away from the tables, and you had to re-arrange the kitchen thus, that it should be near the tables. But the restaurants there were always in one floor - which is a hint, that your kitchen is far from the tables of one floor, i.e. the second floor.
Another reason can be, that your waiting station (the small table) is not placed correctly, and the servers have to wait a long time to reach it.
I strongly suggest you to play the Scenarios first...
