Do I need to invest/deposit?

No, you do not have to invest/deposit.

So, how does StarCoin.ws make money to pay?

We make money from the ads we show, shortlinks ,ptcads ,offerwalls and games.

What are this DM, D, C, M, E on my page ?

Darkmatter DM, Deuterium D, Crystal C, Metal M, Energy E are ingame resources used for ship upgrades, to play games, etc.
Darkmatter DM its the only resource that can be withdrawn.

It's mandatory to own a ship to play ?

If you own a ship/battleship you can access some areas of the game where rewards are bigger, so you will earn faster than without a ship.

How can I withdraw?

You can use for withdraw only Darkmatter (DM) resources.
If you have Deuterium (D) you need to go on Merchant - Resource Market to exchange in Darkmatter (DM)
You can withdraw in Merchant - Export tab