Firstly, against zerg, you need to wall off at the entrance to your natural like seen in this image (any placement will do so long as you leave 1 square of space for one of your units to sit in on hold position) :
Secondly, you need to scout zerg in PvZ, send a probe to his base after you place your first gateway. This is the only edge case in silver league against PvZ that you need to know - when your probe scout reaches his base, if his spawning pool is done or almost done, your running into what is known as a “12 pool” - the fastest attack that a zerg can hit you with.
So in this case you want to get your wall up and chronoboost out a zealot as fast as possible, and build an extra pylon or your likely supply blocked. If you were too slow you can just seal your wall completely with another building then start building adepts or stalkers to shoot the lings from the inside of the wall.