It's the blue folder icon with a white cloud inside. You should find it in the app drawer. The home screen of the app will appear. It's in the left column, toward the bottom of the screen. Several network options will appear. It's near the top of the list. It's near the bottom of the screen. ES File Explorer will scan the network for devices. Computers are listed by IP address. The contents of the folder will appear in ES File Explorer.

Summary:
Connect to the same Wi-Fi network as the shared Windows folder. Open ES File Explorer. Scroll from left to right to move through the welcome pages. Tap START NOW. Tap Network. Tap LAN. Tap Scan. Tap the computer where the shared folder is stored. Log in to the computer if prompted. Tap the folder you want to access.