fleet management and pilots
fleet management
once you have your first aircrafts, pilots and seat configs are assigned automatically. However, as pointed out earlier, I strongly recommend to deactive those "comfort functions" in the settings area.
you can manually assign crews and seat configs by going to the fleet management screen. Just check the boxes for the a/cs you want to edit. While you can assign crews for different a/c types at the same time, this doesn't work for seating configs for obvious reasons.
you can also access the contract page, scheduling page and booked flight schedule from here.
should you receive a "cancellation of flight" notification, go here and hover your mouse over the word "cancelled". It will give you the reason for the cancellation.
pilots
Pilots, by the way, need to be hired from the job market. They are also type-rated, so a pilot with a rating for a Dash Q400 won't be able to operate an A340. You can check if pilots are available on the job market by clicking on pilot management. If there are none available for your required type rating, new pilots will be trained when assiging a crew to an a/c. The training cost is 5-8 times the weekly salary as an initial cost.
On established servers, there are usually enough pilots of most ratings available. However, if there are not, it might be wise to keep checking in here. By 5-8 times the weekly salary costs, it is obviously less expensive to hire pilots when available, even if they are not doing anything for the first 4 or 5 weeks, as training would be more expensive. So if you already know that you will add a/cs of a particular type, you might want to keep that in mind.
BTW, the same goes for firing people. You have to pay a compensation. It is usually better to just keep them when you are planning on using them again within the next couple of weeks.