Hi,

When working team in team, do guys have whole game designed before starting coding, making graphics, etc. or you just do it simultaneously?

Game development is usually a highly iterative process. You design a bit, test it out, make some changes, test some more, update the design etc. Repeat until the work is done.

That's just one way to do it though, there's no one right way. If you ask me, there are some wrong ways though. Designing everything up-front and expecting the design to work out is one of those...

You need enough of a design that you know your destination.  Everybody needs to know what you're trying to create.  

Once you know the target, experiences and comparable projects let everyone know the scale for getting to the destination. In bigger projects there is often negotiation of the target to make sure all the pieces have a scale that works well for the budget.

After that, it is iterative.  Every team, every person, needs their own paths to the destination. It is important to make course corrections frequently. Sometimes you'll find paths blocked and you need to reroute.  These will continue to the same planned destination, only the route to the target changes.

It's ok to have a laid out idea for your game, but once you start working in a team and things start getting created, you'll realize that things might have to evolve and change. And that's ok.