I started using Arduino a few months ago using the web-editor interface installed from
ArduinoCreateAgent-1.1-windows-installer-chrome (1).exe .
Today, I downloaded and installed what I thought was just the newest version of that:
arduino-1.8.6-windows.exe
When I clicked on the desktop icon it had created, I got an interface quite different from the web editor. It had a menu in the upper left above a single window: “Files Edit Sketch Tools Help”. But none of my sketches were there! I clicked on the old icon still in the task bar and found the old interface: the Web Editor complete with all my files.
What is this other interface, how and when should I be using it, and how to I get my sketches into and out of it?
This "other interface" is the Arduino IDE. It's uses this crazy idea of having programs and files on your own computer instead of on other people's computers (AKA "The Cloud"). Very revolutionary! I think it's really going to catch on.
cardani:
how and when should I be using it
As for "how", it's pretty much the same as the Arduino Web Editor (what you call "the old interface"). Things are in different places but pretty much all the features of the Arduino Web Editor are in the Arduino IDE and the Arduino IDE has some very significant additional features (Auto Format, Boards Manager, Burn Bootloader, Upload Using Programmer).
As for "when": Always. The Arduino IDE is far superior to the Arduino Web Editor.
cardani:
how to I get my sketches into and out of it?
Open the sketch in the Arduino Web Editor.
Click on the button with the three dots to the right of the board selection menu
Click "Download Sketch"
Unzip the downloaded sketch
You can now open that sketch in the Arduino IDE via File > Open
To make it more convenient to open your sketches in the Arduino IDE, you might save them to your sketchbook folder. You can find the location of the sketchbook folder at File > Preferences > Sketchbook location. Sketches under the sketchbook folder can be opened via the File > Sketchbook menu.
As for "out of it", well you can save your edits to the sketch via File > Save or File > Save As. Other than that, there is no need to get sketches "out" because they're just files saved on your computer's hard drive. You can copy/move/delete/backup/version control them just like any other file. Amazing, right?