Before starting anything with trailer or vehicle do a visual inspection of both and check all bolts/nuts on wheels, especially the trailer if not used a while
Get trailer set up to be hooked too, check electrical connector plug for loose/fraid wires.
Make sure your hitch ball and insert are connected to vehicle with safety pin in. Now back vehicle to trailer and align trailer hitch with trailer hitch coupler.
Lower trailer onto hitch ball and clamp safety pin down. Check to make sure coupler goes all the way down onto ball. Two safety chains should be on trailer, criss cross these to hitch and connect (this is done incase trailer disconnect will fall onto chains).
Once trailer is set connect electric plug and check all turn signals and brake lights.