You may have been sent a document that uses a LaTeX package that is not already included with the TeX Live installation. The following steps can be used to add the package so the document can be compiled without errors.
The problem can be identified when the document fails to compile and a dialog similar to the following is displayed.
In this case, the missing package is floatrow.
- From the Windows Start Menu, locate the TeX Live group and click the TeX Live Manager shortcut to start the TeX Live Manager program.
- Connect to a repository so the needed files can be located and downloaded. From the tlmgr menu of the TeX Live Manage select Load default (from tlpdb) repository. The selected repository is selected to be near your location.
- Find the floatrow package in the list of packages. You can scroll through the list, or type in a package name in the Match field to reduce the number of packages listed. Turn on the check box next to the floatrow package and then click Install to add the package.
- Wait until the installation is complete, indicated in the status area at the bottom of the dialog. The package is installed and then mktexlsr is run to update the filename database.
- The tlmgr menu can now to used to select Quit.
This completes the steps and you can now compile with the floatrow package available.
Steps to add a package if you are using TeX Live 2019 can be found here: Adding a package to TeX Live 2019 (Windows)