Welcome to the forum! 
First of all, if you want help, then you’re going to have to give us a lot more information than “it doesn’t work”. Please read these two posts below… 
If your network adapter is the Realtek RTL8111/8168/8411, then open up the Manjaro Settings Manager, uninstall the r8168 driver, delete the blacklist for r8169 under /etc/modprobe.d — although removing r8168 should do that automatically already — and reboot.
The r8168 driver module is the driver from Realtek, and it is an out-of-tree module, because the official kernel driver for that chipset is r8169, which is already in the kernel.
The installation of the r8168 driver automatically blacklists r8169, and Manjaro used to do this by default because some people with older hardware were having problems with the in-kernel r8169 driver. But this is no longer applicable, and in fact, it is now r8168 that’s giving people problems. So remove it and use the in-kernel driver.
At least, the above all under the assumption that this is what’s going on with your computer, given that you didn’t provide us with any information. But we’re seeing a lot of issues with this network driver nowadays, so that’s why I’m writing this in advance.