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This is generally at the top of your browser window. The wording may vary on different browsers, but in general you'll see an option for both opening a New Tab and opening a New Window, so select whichever suits your needs. Then enter the URL you want to go to in the address bar and click ↵ Enter (Windows) or ⏎ Return (Mac) to load the new web page.
Locate and click the File option in your browser menu. Select New Window. Wait for the new window/tab to load up.