Getting started with Scheme-it is really easy and there is no cost to you. Simply go to https://www.digikey.com/schemeit/project/ and you will get a pop up.
If you have a Digi-Key log in or would like one you can click on Register/Login. If you just want to try out the software you can click Try It Now and you will enter the software. >Note: You will need a log-in to save or export your schematic.
Here is a capture of the home screen. Hereon the left hand side of your screen you will find Design Starters if you want to work with an existing design or you can select schematic symbols and start a design of your own.
If you are selecting Schematic symbols you can select the category (here I have chosen Amplifiers) and then select an individual symbol. You can simply left-click and drag onto your screen and you have started your schematic.