As an indie dev who are making games mostly as a passion I have a really hard time wrapping myself around the business part, I try to stay away from it to be honest because I find it so boring. There is one thing I sometimes worry about though and that is Trademark. What if I release a game that gets popular and later some giant (like King) does a game and decide to use a name that is close to mine and they get a trademark and decide they want to take me down? I have no protection then, even though I made a big successful game even before they made theirs and got their trademark?

I have a game that is in the same vein and success as for example Hero Siege https://play.google.com/store/apps/details?id=com.panicartstudios.herosiege&hl=en

It seems that game is also made by some single person without a trademark on it. What if some big fish would make a game called "Candy Crush: Heroes Siege" for example now and they trademark that. Could they say he have to take his game down even though he was first?

Going through all the trademark registration things sounds like a real pain and I don't really want to do it if I don't need to. I don't care if anyone else would make a game similair in style or name to mine if they want to so I don't really care about that kind of "protection". But I want to be protected from someone being able to take my game down :/ I am a bit confused on how all this work, could someone enlighten me?

Disclaimer: I'm not a lawyer, and in any case laws vary from place to place.

As far as I understand, there are two types of trade marks, registered and unregistered. I believe you can more or less start using Any TermTM, with the addition those magical little floating letters you are now claiming an unregistered trade mark - provided you're careful not to step on an existing one!

I believe there are certain exemptions for trade marks in the case of something provably established prior to the trade mark.

The bad news is that legal disputes are expensive, and unless you're willing to do all the legal legwork yourself or find someone who will do them for free, you may have extreme difficulty paying for a defence against a big company that insists they own a certain term.

If you're not already familiar with them, I'd recommend researching recent cases where King were attempting to assert their Saga trade mark, and also their attempt to trade mark the term Candy.

Also look at the "Edge" games case.
Trademark mainly applies to titles and logos (and to a lesser extent, character names, place names, etc.) Not to gameplay.
The term "look and feel" is also something to consider. It's not really trademark, and not really copyright (probably closer to trademark).