How should I deal with KiCAD Electrical Rule Check warnings?
Check that you have a &quot;power output&quot; pin driving the +5V net.
These errors typically occur when all that is connected to a power net are &quot;power input&quot; pins of various components, but there's nothing feeding power to the net. There needs to be either a &quot;power output&quot; pin (of a regulator or DC/DC or something), or a PWR_FLAG component connected to the net to mark that the power comes from an external source (such as a connector).
The EEschema manual says:

It is common to have an error or a warning on power pins, even though all seems normal. See example above. This happens because, in most designs, the power is provided by connectors that are not power sources (like regulator output, which is declared as Power out).
The ERC thus won’t detect any Power out pin to control this wire and will declare them not driven by a power source.
To avoid this warning you have to place a &quot;PWR_FLAG&quot; on such a power port. Take a look at the following example:

The error marker will then disappear.
Most of the time, a PWR_FLAG must be connected to GND, because regulators have outputs declared as power out, but ground pins are never power out (the normal attribute is power in), so grounds never appear connected to a power source without a power flag symbol.