Firstly, where you have PWR_FLAG you should put VCC.
Hi bobc! I saw you in so many troubleshooting! Thank you for your help! Nice to meet you! I changed all the power flags but I have the same problem, any other clue?
Thank you again!!!
Luca
Looks like you need a power flag on GND, I usually put this in a corner somewhere:
That solved the problem. Thank you very much!!! I guess some new users will find that interesting.
Do I need to do that every time I use the ground? Will a pad appear in the place where I put the power flag?
Thank you.
Luca
Usually, unless a symbol has a power output and you connect it to GND (e.g. a a power jack).
No, the power flag is never associated with a footprint. It just tells the ERC “don’t flag a ‘not driven’ error for this net”.
What puzzles me is why you don’t get an error for VCC. Is there some more to the schematic?
I generally never directly connect a power symbol to the power flag. While this will get rid of the error message it makes sure that a true error will not be found. (In essence it is the same as clicking “do not check this” would do if such a flag would be an option in kicads erc.)
A better option is to place the power flag as close as possible to where your main supply for that net comes from. For example right at the main power connector. Or on the output of your input filter or fuse.
See ErrType(3): Pin connected to some others pins but no pin to drive it
Obviously, it doesn’t make any difference where you put it.
If you always place it at the true power input then you will discover if you have forgotten to connect something in between. For example by misspelling a label or accidentally selecting the wrong power symbol.
I have seen this happen quite a lot back when i taught students in the use of kicad. They simply spammed power flags until ERC was happy only to later discover that they did not really connect the main connector to part of the board. If you always only connect the flag at the source then you will notice that something is wrong here.
IOW, they didn’t know what they were doing, which was the real problem.
What you are really advising, is don’t put more than one power flag on what should be the same net. It still doesn’t matter where you put it of course.
You are right it does not matter (for ERC)
It is however easier to ensure that you only place one flag if you have a simple rule that tells you where you will place the only one.
I found a very easy (and to me logical) one is to place it directly connected at the source (or as close as possible depending on if you have passives in series).
This also communicates to future readers of your schematic where you intended the main supply to come from. (additional bonus)
Oh and students (or newbies in general) by definition do not yet know what they are doing. After all this is what learning is.
Just out of curiosity, what is this circuit supposed to do? You have the output of the OpAmp connected directly to a power rail. You have the + input of the opamp connected to the power rail through a 10k resistor on one side, and then also connected to the same power rail through another 10k resistor no matter how you have your switch set. Looks like you are trying a comparitor, but your circuit as drawn should do nothing.
Hey there is no more to the schematic. In Vcc actually I will get the power.
The VCC symbol is just a label. It will not have a footprint so you really need to place a connector or anything that can be used to connect power to your board.
Hey there I use this circuit for adding an offset to a signal and magnifying it. It works in my breadboard, I hope it will work on pcb 
Thank you so much!!! I will add it. Thank you again 
Also: Are you aware that all instances of the VCC symbol will be connected? To me it seems you thought this symbol is some sort of connection point instead of a power label. For example pins 2 and 1 of SW1 will be shorted as well as pins 2 and 5.
I need to avoid that! Thank you for warning me. What should I put in order to have different instances?
Power symbols have only one purpose. They globally name nets.
To add a connector (what i assume you want to do) add a conn_01x01 symbol (for a single pin connector) or any other connector symbol (as required by whatever connector part you intent to use)
The test point symbol is another option.
I added another female connector in the op amp output too.