1:When I get to the place I will be camping I connect the sewer hose and then the water connection?
1: Either order, does not matter. However do put a pressure regulator between the park and your rig.. If you are not using a filter put it on the park spigot.. Do not use the cheap sold brass or plastic ones (Save for Camco) use at the minimum the ones with the bright plastic grip on the female end.. Or use a WATTS 1/2 inch or larger with proper adapters. That is the recommended regulator.. Sur-Flo RV regulators work well too.
2:How do I star to use the toilet?
2A: depends on the toilet but with city water you will operate the fill lever,, Just how to do this depends on the unit, ON mine, for example, you LIFT the pedal, on a friends it is one of two levers.
To flush I step on the pedal, he moves BOTH levers.
3:Can I use the toilet if I'm in the road w/o water connection?
3A: Depends. if you have a fresh water supply tank, if you have filled it, if you have a black tank, (If all 3 are correct) then yes, you can.
4: Then when I'm ready to leave the camp site : should I drain everything right?
4A: Right almost, drain everything EXCEPT THE FRESH WATER TANK.
5:The chemicals for toilet/ tank : should I add it to toilet before and after the trip?
5A You sould leave them on the shelf at the dealers.
6:The fridge can not be on while driving right?
6A: much debate, I run with mine on, One factor mine has Direct Spark Ignition thus there is no pilot light to blow out.
7: Are the sewer connections standard ? A: Yes
8: Any hose will fit or I do need an adapter? A: Yes
9: Should I drain the water(grey and black) plus any clean water I got in the trailer if is going to be few weeks store before the next camping trip ?
9A: I drain the black/gray tanks at the end of every campground stay, I did this back when I was part timeing and still do. Fresh it depends.. I kept fresh water in the tank all summer, I only drained it when winterizing, However I kept runing fresh water THROUGH the tank,, That is it was not the same water week after week after week.
10:What else would I need ( beside sewer hose and water pressure regulator)
A really good credit card
(joking) seriously you have the basics covered, Extra (extension) hoses and cords are handy, I carry a full range of power adapters (30 to 50 50 to 30 15 to all the above and 30 to 15) just in cuss.
I like to put a support under the sewer hose so it makes a nice "Smooth" trip to the hole in the ground. That is normally optional.
Depending on your system a toilet tank rinsing wand like the RV-Twister (Which is one of only two I recmmend) may be a good idea.
IT may also not be needed.
OH, one caution.. The waste tank level sensors.. They show EMPTY now.
NEVER expect to see that reading again.. Even if you can shine a flashlight down and see the hose hooked to the bottom, The sensors will show "Stuff" in the tanks.
One omre item.. At your RV store or Camping world they have solid plastic 3" hose "Extensions" they have the proper fitting, they also have elbows, half elbows nd the like. MADE OF CLEAR PLASTIC.
Get one, can be an extension or elbow (I use one of each) this way you can visually verify the tank is EMPTY. More than one person has had a "Robin Williams Moment" when he THOUGHT the flow had ceased.. but it had not.
Sorry so many questions but a trailer has more maintenance than a house