First of all, gather your supplies: Metal fence elements (as many as you need, they come in several widths and heights) ...
... poles, pole-brackets to mount the poles and connectors to connect the fence elements to the poles.
Use the pole-brackets to mount the pole. We had a wooden foundation which was really easy. In case you have a foundation made of stone or concrete, you may need special screws.
Use the connectors to connect the fence elements to the poles.
Building the fence with two elements took about an hour. The middle pole isn't as good as I'd like it to be because I bought the wrong connectors. But it'll keep our dogs out of the neighbour's garden
"Boooooooring..." (He was really not amused by the new fence)