We recommend using GOG GALAXY 2.0 which makes downloading and installing games as convenient as possible. It is easy to use, keeps your games up to date, your downloads can be paused and resumed and - most importantly - it protects your files from being corrupted.
1) GOG GALAXY 2.0 can be downloaded here (https://www.gog.com/galaxy). Once the client has been installed on your system, select a game in your library and click the INSTALL button.
2) Alternatively, you can install your games without a client, using the offline installer:
In order to do so, access your GOG account and library in a browser (https://www.gog.com/account). Select a game, click 'DOWNLOAD OFFLINE BACKUP GAME INSTALLERS' and download all necessary setup files. Open afterwards your download folder and run the install application.
If you experience download corruption issues while downloading via browser, we recommend using a download manager which adds functions such as queuing, pausing and resuming downloads.