Go to https://www.arduino.cc/en/software on a computer (instructions are for Windows 10+ computers) with a USB port and click on Windows 10 and up version. Then, click just download.
Once the software is installed, plug in the provided cable (not the battery wire) to the Arduino Uno and into your computer. When you plug it in, you will be prompted to install some drivers. Accept and install all of them because they are required to make sure the computer works with the Arduino. If it doesn't prompt you to install, continue with the steps and it will eventually prompt you to. Select the dropdown menu and select the port. It may appear as COM3, COM4, COM5 or COM6. Then search for Arduino Uno and select it. You have now connected the Arduino to your computer.
Step 2: Start Programming!
Now you're ready to start programming! Grab your wires and LEDs and get ready.