Katy ~ Welcome to the forum! Congratulations on your "new" trailer. Level ground is sometimes hard to find. I would level the trailer from side to side first. Raise the low side by pulling it onto pieces of scrap lumber (2x6's) or what ever you can find. You may want to buy a set of leveler blocks such as the Lynx levelers and build these into a ramp to get the needed height. They will also come in handy when you go camping. When you get it level, chock the wheels. I prefer to use the chocks that expand between the tandem wheels when in an unlevel area.
When you have that set level the trailer from front to back with the jack. You can use wood under the jack if needed also. I have a plastic cone that works wll for me.
The trailer does have a brake system which is electric and runs from the truck when towing. It can not be used when parked. The magnets would burn up after a few minutes of operation.