There can be many pieces that make up the panels of your fence.
Stringers are the pieces that run horizontally between the posts and support the fence boards. Where these go on your fence depends on your fence design.
Allow at least a couple of inches below the bottom stringer to prevent rot and to make it easier to mow.
One way to attach the stringers is to cut them to fit in between the posts and toe nail them to the posts.
You can also dado out a section of the post and set stringers in flush with it.
Always used galvanized nails on any project that will come in contact with moisture.
Install the stringers square, and be don't knock your posts out of plumb.
Your fence panels can be any design you want. You can put up vertical pickets, lattice, or pre-made panels. It looks best if you keep all the panels consistent and symmetrical.
Building a Gate
Plan on leaving at least a quarter inch space on each side of your gate for swinging clearance.
It helps to build the gate on a flat piece of plywood or particleboard.
For this picket fence gate, we used two cross pieces and a diagonal piece for support. Nail these pieces to the plywood, then nail them to each other.
Attach your panel design to the support pieces. In our case it was pickets.
Take out the nails holding the gate to the plywood.
Set the gate in place using blocks to set it at the right height and spacers to keep it the proper distance from the posts.
Use strong corrosive-resistant hardware and screws to attach the gate to the posts.