Where does robots.txt need to go?
At the root of each host, such as https://example.com/robots.txt. A file in a subfolder is ignored, and each subdomain, such as blog.example.com, needs its own file. The name must be lowercase.
Will Disallow remove a page from Google?
No. Disallow stops crawling, but a blocked URL can still be indexed from links on other sites. To remove a page from search, let it be crawled and add a noindex meta tag or X-Robots-Tag header, then wait for Google to recrawl it.
How do Allow and Disallow conflicts get resolved?
Google and Bing follow the most specific rule, meaning the one with the longest matching path. If the two match with equal length, Allow wins. So "Disallow: /docs/" with "Allow: /docs/public/" blocks everything under /docs/ except the public folder.
Does Google respect Crawl-delay?
No. Googlebot ignores Crawl-delay and adjusts its rate automatically based on how your server responds. Bing and some other crawlers do honor it. If Google is crawling too fast, return 503 or 429 responses temporarily rather than relying on robots.txt.
Should I block my admin or login pages?
You can, but robots.txt is public, so listing a secret path in it reveals that path to anyone who reads the file. Protect private areas with authentication, and use Disallow only to save crawl effort on pages that have no search value.