Welcome, Faith! I know of three ways to input Greek characters.
(1) The Polytonic Greek keyboard layout in Windows. See this guide
on how to set that up. Be warned, this keyboard layout is quite complicated.
. The keyboard layout is much simpler here, but you have to copy text from the site to wherever you want it.
Or (3) you could pay $24 for Tavultesoft Keyman and download the Classical Greek keyboard layout from their site. This layout is almost identical to the one at Type Greek, and like the Windows keyboard layout it can be used anywhere without any copying and pasting.
I used method 2 for a while but eventually saw that Keyman was worth the price for me. I'm sure there are other methods, but these are the ones I've found.