Hello,
I need help about ERC errors. So I copy sscheme from internet and everything seems connected like on original scheme. Do I need to resolve this errors or they can stay like that? Can they effect in real life or that errors are just in simulation?
You have several issues here.
You have errors on unconnected pins.
And you have errors on power pins.
Both are easy to fix, just check the schematic and look for “floating” pins and add an “X” symbol to them (right side menu). The power errors can usually be fixed by adding a “PWR_FLAG” to the pin.
The simulation errors are more difficult, you’ll need to add (or edit) the sim models to the parts in question.
Thank you very much, it worked! But i only don’t understand why it says error if my GND pin from amplifier goes to - pole of battery. When I add an PWR_FLAG to that pin it doesn’t show any errors.
Your U1 pin 4 is is labeled a “power input”. Look at the properties of the pin.
The Kicad battery symbol has both pin properties (+ve and -ve) labeled as “passive”. Check pin properties to confirm.
The ECR is not real smart.
If a passive pin is connected to a power input pin, ERC will show an error.
If a power output pin is connected to a power input pin, ERC is happy.
By adding a power flag to the battery -ve pin you are changing the use of that pin from passive to power out, so ERC is happy.
You could also copy the battery symbol to a personal library and then change the electrical properties of the pin to “Power out”, then use that new version of the battery symbol on the schematic and the ERC would be happy, without you needing to use power flags.
Just for kicks, place a fuse (or current limiting resistor) between the -ve battery and U pin 4.
You will get another ERC error because the poor ERC has no conception of a fuse. To the ERC, a fuse is just something blocking the path between the battery -ve “power out” and the U pin 4 “Power in”, so you use another power flag to tell the ERC that the fuse symbol is OK. 
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