mac with globe and caution symbol will not go away and cannot get into my computer

I got this macbook air from another person and the disk password kept popping up which I did not have. I saw something that said worst comes to worst u unlock the “fire vault” then delete the disk. I don’t know rly what I’m doing. My laptop is now stuck in this screen with “support.apple.com/mac/startup” yet I don’t get anymore info from that. Help please?