If you're using your phone, i would suggest downloading the SwiftKey Keyboard app - it has a really nice and user-friendly Hebrew keyboard. If you're using a Mac, go to System Preferences and click on Languages & Regions, and then add Hebrew to the list of languages on the left-hand side. On a Windows computer, it depends which version you have. Sometimes it will be in Settings, other times in Control Panel. I would suggest googling it and specifying which version of Windows you're using.
Go to your keyboard, hit the settings symbol, select languages and check hebrew