There could be a few reasons why the first tab that opens when you launch Google Chrome is Minesweeper. One possibility is that someone has set Minesweeper as your homepage. To check if this is the case, go to the Chrome settings menu and look under the "On startup" section. If "Open the New Tab page" is selected, then Minesweeper is likely not your homepage.
Another possibility is that a Chrome extension is causing Minesweeper to open as your first tab. To check if this is the case, go to the Chrome settings menu and click on "Extensions." If you see any suspicious extensions listed, try disabling or removing them.
Finally, it's also possible that Minesweeper is opening because of a virus or other malware. If you suspect that this is the case, you should scan your computer with a trusted antivirus program.