api-ms-win-crt-runtime-l1-1-0.dll library is intended to provide a stable work for C based applications for Windows 7, 8, and 10. When it is missing, it is completely impossible to run some programs like Skype for example, which can become a serious problem especially if you are in emergency. However, this problem can be easily solved. 

Should I Download api-ms-win-crt-runtime-l1-1-0.dll Separately?
Yes, you can do this. However, make sure you provide api-ms-win-crt-runtime-l1-1-0.dll download only from reputable and credible website, otherwise you are risking to get your Windows corrupted or even get a malware on your PC. The thing is that some services are modifying the library - and this is not always good for you as a PC user. However, if you want to be guaranteed the result is going to be positive make sure you either download the library from good website or get the file from the original provider. 

How to Fix api-ms-win-crt-runtime-l1-1-0.dll Using Microsoft Official Website? 

There are two possible reasons for the mistake to appear:
incorrect installation of Visual C++ Redistributable 2017
incorrect installation (or absence) of KB2999226 update
Both reasons could be solved with downloading and installing corresponding software from the official Microsoft website. However, it is better to let PC make updates on the schedule like it is offered by the OS constantly, so if you want to avoid such problems in future just allow the OS to make updates. 

However, the most common reason is the absence of KB2999226 update, so you need to try this one first. Just find it on the Microsoft website (do not even think about downloading it from somewhere else) or follow the link: https://support.microsoft.com/en-us/help/2999226/update-for-universal-c-runtime-in-windows and download the updated version for your Windows. If you have Windows 10 then you do not need to download this update at all. 

Then you have to install the update, wait until the computer reboots, and try to launch the program again. If it did not help or if you have Windows 10, then you need to install Visual C++ Redistributable 2017 on your computer. You can do this on the Microsoft website here: https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads (download the latest version for your system version). 

Important: Download x86 and x64 version for 64-bit system version computer and only x86 for 32-bit version computer. 

Afterwards, you need to install the software and reboot the personal computer. The next attempt to run the program you had problems with will be successful. 

Actually, it is a bad idea for regular user to get involved into the issues with .dll files, however, if you follow the instruction and manage to avoid mistakes, there are high chances the problem will be solved. 

The .dll issues are claimed to be easy ones, compared to death screen error, for example, as those can be managed by professionals only, and not by users.